County GIS · State lines · October 20, 2026
Idaho–Montana Border Counties: Parcel Maps on Both Sides
All 16 counties on the Idaho–Montana line, with seats, 2023 populations and a link to each official parcel map, plus what changes at the state line.
Looking for the counties on the Idaho–Montana border and their parcel maps? According to the Census Bureau's county adjacency file, 8 Idaho counties touch 8 Montana counties along the line. Each one keeps its own property records and its own parcel viewer, so land near the line often means checking two counties in two states.
A farm, hunting tract or lake lot can sit in one state while the road, the neighbors or the rest of the property are in the other. This page lists every county that touches the line on either side, with links to each official parcel map.
Idaho–Montana border at a glance
- Counties on the line: 16 (8 in Idaho, 8 in Montana)
- With a verified public parcel viewer in our directory: 16 of 16
- Residents, 2023 estimates: about 130,672 on the Idaho side and 356,071 on the Montana side
- Most populous on each side: Bonner County, ID (52,547) and Gallatin County, MT (126,409)
- Largest by land area: Idaho County, ID (8,477 sq mi) and Beaverhead County, MT (5,543 sq mi)
Idaho counties on the line
| County | Seat | Land (sq mi) | 2023 pop. | Parcel viewer |
|---|---|---|---|---|
| Bonner County | Sandpoint | 1,733 | 52,547 | county web map |
| Boundary County | Bonners Ferry | 1,269 | 13,557 | ArcGIS Experience Builder |
| Clark County | Dubois | 1,763 | 801 | Idaho statewide Parcels layer in ArcGIS Map Viewer |
| Clearwater County | Orofino | 2,457 | 9,214 | Idaho statewide Parcels layer in ArcGIS Map Viewer |
| Fremont County | St. Anthony | 1,864 | 14,196 | Idaho statewide Parcels layer in ArcGIS Map Viewer |
| Idaho County | Grangeville | 8,477 | 17,890 | ArcGIS Web AppBuilder |
| Lemhi County | Salmon | 4,564 | 8,441 | ArcGIS Experience Builder |
| Shoshone County | Wallace | 2,637 | 14,026 | ArcGIS Experience Builder |
Montana counties on the line
| County | Seat | Land (sq mi) | 2023 pop. | Parcel viewer |
|---|---|---|---|---|
| Beaverhead County | Dillon | 5,543 | 9,885 | ArcGIS Experience Builder |
| Gallatin County | Bozeman | 2,605 | 126,409 | ArcGIS Experience Builder |
| Lincoln County | Libby | 3,613 | 21,895 | ArcGIS Web AppBuilder |
| Madison County | Virginia City | 3,588 | 9,521 | ArcGIS Experience Builder |
| Mineral County | Superior | 1,220 | 5,090 | ArcGIS Experience Builder |
| Missoula County | Missoula | 2,593 | 121,849 | county web map |
| Ravalli County | Hamilton | 2,391 | 47,738 | ArcGIS Map Viewer |
| Sanders County | Thompson Falls | 2,760 | 13,684 | ArcGIS Instant Apps |
Which counties face each other
The Census adjacency file pairs counties that share a boundary. Use it to find the county across the line from the one you know:
- Bonner County, ID borders Lincoln County, MT, Sanders County, MT
- Boundary County, ID borders Lincoln County, MT
- Clark County, ID borders Beaverhead County, MT
- Clearwater County, ID borders Mineral County, MT, Missoula County, MT
- Fremont County, ID borders Beaverhead County, MT, Gallatin County, MT, Madison County, MT
- Idaho County, ID borders Missoula County, MT, Ravalli County, MT
- Lemhi County, ID borders Beaverhead County, MT, Ravalli County, MT
- Shoshone County, ID borders Mineral County, MT, Sanders County, MT
What changes when you cross the line
- Different viewers. On the Idaho side the official maps run on: ArcGIS Experience Builder (3); Idaho statewide Parcels layer in ArcGIS Map Viewer (3); county web map (1); ArcGIS Web AppBuilder (1). On the Montana side: ArcGIS Experience Builder (4); ArcGIS Web AppBuilder (1); county web map (1); ArcGIS Map Viewer (1); ArcGIS Instant Apps (1). Search boxes, parcel ID formats and the details shown in pop-ups will differ.
- Different records offices. Deeds, plats and tax bills are kept by the county where the parcel sits.
- Different rules. Zoning, septic permits and property tax are set locally and by each state, so check with the county on the side where you plan to build or buy.
Researching a tract that crosses the line
- Find the parcel in both counties' viewers. Each side will show only its own piece, with its own parcel number.
- Pull the recorded deed from each county's register or recorder, since each county records only the land inside its own boundary.
- Expect two tax bills, one from each county, and check each state's rules for homestead or farm exemptions.
- For a sale, a fence or a building permit, hire a licensed surveyor familiar with the line; tax-map lines are drawings, not surveys.
A quick way to check which side a spot is on
Open the Platbookmapper Land Map, search the nearest county, and tap the spot. The land report shows which county it falls in, along with flood zone, elevation, soil and wetlands, and links to that county's parcel map.
Related guides
More: Idaho counties · Montana counties
Sources
- U.S. Census Bureau county adjacency file, used for which counties share the line.
- U.S. Census Bureau Gazetteer files, 2020 county land area.
- U.S. Census Bureau, Population Estimates Program, county totals, Vintage 2023 (July 1, 2023 estimates)
- Platbookmapper county GIS directory (live data file behind our county pages, pulled October 20, 2026) for each county's official parcel viewer.
- County seats: Wikidata (county seat property), cross-checked against Census place names.