diff --git a/api/group.py b/api/group.py
index 5399ce10..962870c1 100644
--- a/api/group.py
+++ b/api/group.py
@@ -27,10 +27,12 @@
 from db.group import Group
 from schemas.group import UpdateGroup, CreateGroup, GroupResponse
 from services.crud_helper import model_patcher, model_deleter, model_adder
-from services.query_helper import (
-    simple_get_by_id,
-    paginated_all_getter,
+from services.group_helper import (
+    get_well_counts_by_group_id,
+    group_to_response,
+    paginated_groups_getter,
 )
+from services.query_helper import simple_get_by_id
 
 router = APIRouter(prefix="/group", tags=["group"])
 
@@ -74,7 +76,7 @@ def get_groups(
     """
     Retrieve all groups from the database.
     """
-    return paginated_all_getter(session, Group, filter_=filter_)
+    return paginated_groups_getter(session, filter_=filter_)
 
 
 @router.get("/{group_id}", summary="Get group by ID")
@@ -84,7 +86,9 @@ def get_group_by_id(
     """
     Retrieve a group by ID from the database.
     """
-    return simple_get_by_id(session, Group, group_id)
+    group = simple_get_by_id(session, Group, group_id)
+    counts = get_well_counts_by_group_id(session, [group.id])
+    return group_to_response(group, counts.get(group.id, 0))
 
 
 # @router.get(
diff --git a/docs/refine-json-filters-and-virtual-fields.md b/docs/refine-json-filters-and-virtual-fields.md
index e00a7c20..cd393cdc 100644
--- a/docs/refine-json-filters-and-virtual-fields.md
+++ b/docs/refine-json-filters-and-virtual-fields.md
@@ -38,6 +38,7 @@ Associations are stored in **`ThingContactAssociation`** (`thing_id`, `contact_i
 | List resource | Virtual `field` | Meaning | Implementation sketch |
 |---------------|------------------|---------|------------------------|
 | Thing (wells) | `contacts` | “Does **any** linked contact’s **name** match?” | EXISTS over `ThingContactAssociation` joining `Contact`, predicate on **`Contact.name`** |
+| Thing (wells) | `groups` | “Does **any** linked project (**Group**) match?” | EXISTS over `GroupThingAssociation` joining `Group`, predicate on **`Group.id`** or **`Group.name`** |
 | Contact | `things` | “Does **any** linked monitoring site (**thing**) **name** match?” | EXISTS over **`ThingContactAssociation`** joining **`Thing`**, predicate on **`Thing.name`** |
 
 We keep naming aligned with ORM accessors (`Thing.contacts`-style summaries in API responses use **contacts**, and **`Contact`** side uses **`things`** for parity with the association proxy).
@@ -77,6 +78,7 @@ Those paths previously raised **500**. Virtual sorts are implemented in **`_appl
 | `monitoring_status`, `well_status`, `datalogger_suitability_status` | Same “latest open” **`StatusHistory.status_value`** subquery as filters; **`lower(...)`**, **`nulls_last`** |
 | `site_name` | **`ThingIdLink.alternate_id`** where **`alternate_organization = 'NMBGMR'`**, smallest link **`id`** (matches **`Thing.site_name`**) |
 | `contacts` | **`min(lower(Contact.name))`** over **`ThingContactAssociation`** (first name alphabetically among linked contacts) |
+| `groups` | **`min(lower(Group.name))`** over **`GroupThingAssociation`** (first project name alphabetically among linked groups) |
 | `aquifers` | **`min(lower(AquiferSystem.name))`** over **`ThingAquiferAssociation`** |
 | `open_status` | Latest open **“Open Status”** row; rank **Open** before **Closed**, then unknown strings, then no row |
 | `measuring_point_height` | Latest **`MeasuringPointHistory`** row with non-null height (**`start_date` desc**, limit 1) |
@@ -104,6 +106,7 @@ Each filter **must** include **`field`**, **`operator`**, and **`value`** keys (
 | Merge **`filter_`** + **`filters`**, sorting, pagination hook | **`order_sort_filter`** in **`services/query_helper.py`** |
 | Dispatch virtual fields | **`_apply_json_filter_clause`** in **`services/query_helper.py`** |
 | **`Thing` + contacts** | **`_apply_thing_contacts_filter`** |
+| **`Thing` + groups** | **`_apply_thing_groups_filter`** |
 | **`Contact` + things** | **`_apply_contact_things_filter`** |
 | Contact list accepts repeated **`filter`** | **`GET`** **`/contact`** in **`api/contact.py`**, **`get_db_contacts`** in **`services/contact_helper.py`** |
 | Wells list pattern (reference) | **`GET`** **`/thing/water-well`** in **`api/thing.py`**, **`get_db_things`** in **`services/thing_helper.py`** |
@@ -113,6 +116,7 @@ Each filter **must** include **`field`**, **`operator`**, and **`value`** keys (
 
 - **`tests/test_contact_filters.py`**: **`things`** filters, **`things`** sort, multiple **`filter`** params on **`GET /contact`**.
 - **`tests/test_thing.py`** (contacts on wells): **`contacts`** **`contains`**, **`ncontains`**, **`nnull`**, and **`sort`** on **`monitoring_status`**, **`site_name`**, **`contacts`**, **`aquifers`**, etc.
+- **`tests/test_thing.py`** (groups on wells): **`groups`** **`eq`** by project id or name when filtering wells by project.
 
 ## When you change this
 
diff --git a/schemas/group.py b/schemas/group.py
index e3cc7488..2472dc0f 100644
--- a/schemas/group.py
+++ b/schemas/group.py
@@ -58,6 +58,7 @@ class GroupResponse(BaseResponseModel):
     project_area: str | None
     group_type: GroupType | None
     parent_group_id: int | None
+    well_count: int = 0
 
     @model_validator(mode="before")
     def project_area_to_wkt(self: Self) -> Self:
diff --git a/services/group_helper.py b/services/group_helper.py
new file mode 100644
index 00000000..b81dd81c
--- /dev/null
+++ b/services/group_helper.py
@@ -0,0 +1,65 @@
+# ===============================================================================
+# Copyright 2025 ross
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ===============================================================================
+from typing import Any
+
+from fastapi_pagination.ext.sqlalchemy import paginate
+from sqlalchemy import func, select
+from sqlalchemy.orm import Session
+
+from db.group import Group, GroupThingAssociation
+from db.thing import Thing
+from schemas.group import GroupResponse
+from services.query_helper import order_sort_filter
+
+
+def get_well_counts_by_group_id(
+    session: Session, group_ids: list[int]
+) -> dict[int, int]:
+    if not group_ids:
+        return {}
+
+    stmt = (
+        select(
+            GroupThingAssociation.group_id,
+            func.count(Thing.id),
+        )
+        .join(Thing, GroupThingAssociation.thing_id == Thing.id)
+        .where(GroupThingAssociation.group_id.in_(group_ids))
+        .where(Thing.thing_type == "water well")
+        .group_by(GroupThingAssociation.group_id)
+    )
+    return {row[0]: int(row[1]) for row in session.execute(stmt).all()}
+
+
+def group_to_response(group: Group, well_count: int = 0) -> GroupResponse:
+    response = GroupResponse.model_validate(group)
+    return response.model_copy(update={"well_count": well_count})
+
+
+def paginated_groups_getter(
+    session: Session,
+    filter_: str | None = None,
+    *,
+    filters: list[str] | None = None,
+) -> Any:
+    sql = select(Group)
+    sql = order_sort_filter(sql, Group, None, None, filter_, filters=filters)
+
+    def transformer(groups: list[Group]) -> list[GroupResponse]:
+        counts = get_well_counts_by_group_id(session, [group.id for group in groups])
+        return [group_to_response(group, counts.get(group.id, 0)) for group in groups]
+
+    return paginate(query=sql, conn=session, transformer=transformer)
diff --git a/services/query_helper.py b/services/query_helper.py
index 538e93a0..aeb14227 100644
--- a/services/query_helper.py
+++ b/services/query_helper.py
@@ -343,6 +343,25 @@ def _thing_contacts_min_name_sort_scalar(thing_table: type):
     )
 
 
+def _thing_groups_min_name_sort_scalar(thing_table: type):
+    """Minimum ``lower(Group.name)`` across linked projects (stable proxy for display order)."""
+    from db.group import Group, GroupThingAssociation
+
+    gta = GroupThingAssociation
+    g = Group
+    return (
+        select(func.min(func.lower(g.name)))
+        .select_from(gta)
+        .join(g, gta.group_id == g.id)
+        .where(
+            gta.thing_id == thing_table.id,
+            g.name.isnot(None),
+        )
+        .correlate(thing_table)
+        .scalar_subquery()
+    )
+
+
 def _thing_aquifers_min_name_sort_scalar(thing_table: type):
     """Minimum ``lower(AquiferSystem.name)`` across linked aquifers."""
     from db.aquifer_system import AquiferSystem
@@ -417,6 +436,7 @@ def _contact_things_min_name_sort_scalar(contact_table: type):
         "datalogger_suitability_status",
         "site_name",
         "contacts",
+        "groups",
         "aquifers",
         "open_status",
         "measuring_point_height",
@@ -486,6 +506,9 @@ def num_order(expr):
     if sort == "contacts":
         return str_order(_thing_contacts_min_name_sort_scalar(thing_table))
 
+    if sort == "groups":
+        return str_order(_thing_groups_min_name_sort_scalar(thing_table))
+
     if sort == "aquifers":
         return str_order(_thing_aquifers_min_name_sort_scalar(thing_table))
 
@@ -610,6 +633,91 @@ def _linked_contact_select(predicate):
     return sql.where(exists(_linked_contact_select(pred)))
 
 
+def _apply_thing_groups_filter(
+    sql: Select[Any],
+    thing_table: type,
+    operator: str,
+    value: Any,
+) -> Select[Any]:
+    """Filter ``Thing`` rows using linked groups / projects (many-to-many).
+
+    Refine sends ``field=groups`` from the wells list when filtering by project.
+    Match **any** linked ``Group`` by id (numeric ``eq``) or by ``Group.name``.
+    """
+    from db.group import Group, GroupThingAssociation
+
+    gta = GroupThingAssociation
+    g = Group
+
+    def _linked_group_select(predicate):
+        return (
+            select(1)
+            .select_from(gta)
+            .join(g, gta.group_id == g.id)
+            .where(
+                gta.thing_id == thing_table.id,
+                predicate,
+            )
+        )
+
+    any_linked_group = (
+        select(1)
+        .select_from(gta)
+        .join(g, gta.group_id == g.id)
+        .where(gta.thing_id == thing_table.id)
+    )
+
+    if operator == "nnull":
+        return sql.where(exists(any_linked_group))
+
+    if operator == "null":
+        return sql.where(~exists(any_linked_group))
+
+    if operator == "eq":
+
+        def _eq_predicate():
+            try:
+                group_id = int(value)
+                return g.id == group_id
+            except (TypeError, ValueError):
+                return g.name == str(value)
+
+        return sql.where(exists(_linked_group_select(_eq_predicate())))
+
+    if operator == "ne":
+
+        def _ne_predicate():
+            try:
+                group_id = int(value)
+                return g.id == group_id
+            except (TypeError, ValueError):
+                return g.name == str(value)
+
+        return sql.where(~exists(_linked_group_select(_ne_predicate())))
+
+    if operator == "ncontains":
+        nlg = _linked_group_select(g.name.ilike(f"%{value}%"))
+        return sql.where(~exists(nlg))
+
+    if operator == "contains":
+        pred = g.name.ilike(f"%{value}%")
+    elif operator == "startswith":
+        pred = g.name.ilike(f"{value}%")
+    elif operator == "endswith":
+        pred = g.name.ilike(f"%{value}")
+    else:
+        raise HTTPException(
+            status_code=400,
+            detail=(
+                f"Operator {operator!r} is not supported for groups "
+                "filters (contains, ncontains, eq, ne, startswith, endswith, "
+                "null, nnull)"
+            ),
+        )
+
+    return sql.where(exists(_linked_group_select(pred)))
+
+
 def _apply_contact_things_filter(
     sql: Select[Any],
     contact_table: type,
@@ -739,6 +847,9 @@ def _apply_json_filter_clause(
     if getattr(table, "__name__", None) == "Thing" and field == "contacts":
         return _apply_thing_contacts_filter(sql, table, operator, value)
 
+    if getattr(table, "__name__", None) == "Thing" and field == "groups":
+        return _apply_thing_groups_filter(sql, table, operator, value)
+
     try:
         column = getattr(table, field)
     except AttributeError as exc:
diff --git a/services/thing_helper.py b/services/thing_helper.py
index 16fdd9a6..c7500045 100644
--- a/services/thing_helper.py
+++ b/services/thing_helper.py
@@ -71,6 +71,7 @@ def is_debug_timing_enabled() -> bool:
     selectinload(Thing.contact_associations).selectinload(
         ThingContactAssociation.contact
     ),
+    selectinload(Thing.group_associations).selectinload(GroupThingAssociation.group),
     selectinload(Thing.well_purposes),
     selectinload(Thing.well_casing_materials),
     selectinload(Thing.links),
diff --git a/tests/test_group.py b/tests/test_group.py
index d703b0bd..de4c6672 100644
--- a/tests/test_group.py
+++ b/tests/test_group.py
@@ -5,7 +5,8 @@
 from pydantic import ValidationError
 
 from core.dependencies import admin_function, viewer_function, editor_function
-from db import Group
+from db import Group, GroupThingAssociation, Thing
+from db.engine import session_ctx
 from main import app
 from schemas import DT_FMT
 from schemas.group import ValidateGroup
@@ -103,6 +104,55 @@ def test_get_groups(group):
     assert data["items"][0]["project_area"] == to_shape(group.project_area).wkt
     assert data["items"][0]["description"] == group.description
     assert data["items"][0]["parent_group_id"] == group.parent_group_id
+    assert data["items"][0]["well_count"] == 1
+
+
+def test_get_groups_well_count_excludes_non_water_wells(
+    group, water_well_thing, location, spring_thing
+):
+    with session_ctx() as session:
+        second_well = Thing(
+            name="Second Test Well",
+            first_visit_date="2023-03-03",
+            thing_type="water well",
+            release_status="draft",
+            well_depth=10,
+            hole_depth=10,
+            well_casing_diameter=5.0,
+            well_casing_depth=10.0,
+        )
+        session.add(second_well)
+        session.commit()
+        session.refresh(second_well)
+
+        for thing_id in (second_well.id, spring_thing.id):
+            session.add(GroupThingAssociation(group_id=group.id, thing_id=thing_id))
+        session.commit()
+
+    response = client.get("/group")
+    assert response.status_code == 200
+    data = response.json()
+    item = next(item for item in data["items"] if item["id"] == group.id)
+    assert item["well_count"] == 2
+
+
+def test_get_groups_well_count_zero_without_associations():
+    payload = {
+        "release_status": "private",
+        "name": "Empty Project Group",
+        "description": "No associated wells.",
+    }
+    create_response = client.post("/group", json=payload)
+    assert create_response.status_code == 201
+    group_id = create_response.json()["id"]
+
+    response = client.get("/group")
+    assert response.status_code == 200
+    data = response.json()
+    item = next(item for item in data["items"] if item["id"] == group_id)
+    assert item["well_count"] == 0
+
+    cleanup_post_test(Group, group_id)
 
 
 def test_get_group_by_id(group):
@@ -118,6 +168,7 @@ def test_get_group_by_id(group):
     assert data["description"] == group.description
     assert data["parent_group_id"] == group.parent_group_id
     assert data["release_status"] == group.release_status
+    assert data["well_count"] == 1
 
 
 def test_get_group_by_id_404_not_found(group):
diff --git a/tests/test_thing.py b/tests/test_thing.py
index d3444a7c..8c8859c4 100644
--- a/tests/test_thing.py
+++ b/tests/test_thing.py
@@ -985,6 +985,67 @@ def test_get_water_wells_filter_contacts_nnull(water_well_thing, contact):
     assert water_well_thing.id in ids
 
 
+def test_get_water_wells_filter_groups_eq_by_id(group, water_well_thing):
+    fl = json.dumps(
+        {"field": "groups", "operator": "eq", "value": str(group.id)},
+    )
+    response = client.get("/thing/water-well", params=[("filter", fl)])
+    assert response.status_code == 200
+    data = response.json()
+    ids = [item["id"] for item in data["items"]]
+    assert water_well_thing.id in ids
+
+
+def test_get_water_wells_filter_groups_eq_by_id_no_match(group, water_well_thing):
+    fl = json.dumps(
+        {"field": "groups", "operator": "eq", "value": "999999"},
+    )
+    response = client.get("/thing/water-well", params=[("filter", fl)])
+    assert response.status_code == 200
+    data = response.json()
+    ids = [item["id"] for item in data["items"]]
+    assert water_well_thing.id not in ids
+
+
+def test_get_water_wells_filter_groups_eq_by_name(group, water_well_thing):
+    fl = json.dumps(
+        {"field": "groups", "operator": "eq", "value": group.name},
+    )
+    response = client.get("/thing/water-well", params=[("filter", fl)])
+    assert response.status_code == 200
+    data = response.json()
+    ids = [item["id"] for item in data["items"]]
+    assert water_well_thing.id in ids
+
+
+def test_get_water_wells_filter_groups_unsupported_operator(group):
+    fl = json.dumps(
+        {"field": "groups", "operator": "gt", "value": group.id},
+    )
+    response = client.get("/thing/water-well", params=[("filter", fl)])
+    assert response.status_code == 400
+
+
+def test_get_water_wells_list_includes_groups(group, water_well_thing):
+    response = client.get("/thing/water-well", params={"page": 1, "size": 50})
+    assert response.status_code == 200
+    data = response.json()
+    well = next(item for item in data["items"] if item["id"] == water_well_thing.id)
+    assert len(well["groups"]) >= 1
+    assert well["groups"][0]["name"] == group.name
+
+
+def test_get_water_wells_sort_groups_asc(group, water_well_thing):
+    response = client.get(
+        "/thing/water-well",
+        params={
+            "sort": "groups",
+            "order": "asc",
+        },
+    )
+    assert response.status_code == 200
+
+
 def test_get_water_wells_sort_monitoring_status_desc(water_well_thing):
     """Derived status columns are Python properties; sort uses StatusHistory SQL."""
     response = client.get(