County GIS · State lines · October 20, 2026

Colorado–New Mexico Border Counties and Their Parcel Maps

All 12 counties on the Colorado–New Mexico 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 Colorado–New Mexico border and their parcel maps? According to the Census Bureau's county adjacency file, 7 Colorado counties touch 5 New Mexico 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.

Colorado–New Mexico border at a glance

• Counties on the line: 12 (7 in Colorado, 5 in New Mexico)
• With a verified public parcel viewer in our directory: 11 of 12
• Residents, 2023 estimates: about 125,968 on the Colorado side and 211,175 on the New Mexico side
• Most populous on each side: La Plata County, CO (56,407) and San Juan County, NM (120,675)
• Largest by land area: Las Animas County, CO (4,773 sq mi) and Rio Arriba County, NM (5,861 sq mi)

Colorado counties on the line

New Mexico counties on the line

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:

• Archuleta County, CO borders Rio Arriba County, NM, San Juan County, NM
• Baca County, CO borders Union County, NM
• Conejos County, CO borders Rio Arriba County, NM, Taos County, NM
• Costilla County, CO borders Colfax County, NM, Taos County, NM
• La Plata County, CO borders San Juan County, NM
• Las Animas County, CO borders Colfax County, NM, Union County, NM
• Montezuma County, CO borders San Juan County, NM

What changes when you cross the line

• Different viewers. On the Colorado side the official maps run on: ArcGIS (2); no verified public viewer listed yet (1); ArcGIS Experience Builder (1); county web map (1); ArcGIS Web AppBuilder (1); Colorado Public Parcel Map (1). On the New Mexico side: NM Office of the State Engineer County Parcels 2025 layer in ArcGIS Map Viewer (4); ArcGIS Web AppBuilder (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

1. Find the parcel in both counties' viewers. Each side will show only its own piece, with its own parcel number.
2. Pull the recorded deed from each county's register or recorder, since each county records only the land inside its own boundary.
3. Expect two tax bills, one from each county, and check each state's rules for homestead or farm exemptions.
4. 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

Tap the spot on the Platbookmapper Land Map. Its land report names the county and links straight to that county's parcel viewer, plus FEMA flood, USGS elevation, USDA soil and wetland results.

Related guides

• Colorado county GIS websites by viewer
• Colorado plat maps
• New Mexico county GIS websites by viewer

More: Colorado counties · New Mexico 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.