Union County is a county in New Mexico, United States, on the high plains of the state’s northeastern corner, where it borders Colorado, Oklahoma and Texas. It had a population of 4,079 at the 2020 census and covers 3,831 square miles (9,920 km2) — 3,824 square miles (9,900 km2) of land and 7.1 square miles (18 km2) of water — centred near 36°29′N 103°28′W.
Clayton is the county seat, and its postal code is 88415. The county has one incorporated town (Clayton), three incorporated villages (Des Moines, Folsom and Grenville), and a handful of small unincorporated communities. Union County observes Mountain Time and has no civil townships.
Towns & Villages in Union County
Union County is sparsely settled — the whole county averages about one resident per square mile, and the great majority of that population lives in and around Clayton. The table below covers the incorporated town and villages plus the unincorporated communities named on county maps; “Unincorp.” places have no municipal government and are typically a rail siding, ranch crossroads, or a handful of houses.
| Place | Type | Pop. | ZIP |
|---|---|---|---|
| Clayton | Town · seat | — | 88415 |
| Des Moines | Village | — | 88418 |
| Folsom | Village | — | 88419 |
| Grenville | Village | — | 88424 |
| Capulin | CDP | — | 88414 |
| Amistad | Unincorp. | — | 88410 |
| Gladstone | Unincorp. | — | 88422 |
| Sedan | Unincorp. | — | 88436 |
| Hayden | Unincorp. | — | — |
| Mount Dora | Unincorp. | — | — |
| Seneca | Unincorp. | — | — |
| Sofia | Unincorp. | — | — |
| McNees Crossing | Unincorp. | — | — |
ZIP Codes
- 88415 — Clayton (also serves Mount Dora and McNees Crossing)
- 88418 — Des Moines
- 88419 — Folsom
- 88424 — Grenville
- 88414 — Capulin
- 88422 — Gladstone
- 88410 — Amistad
- 88436 — Sedan
Hayden, Seneca and Sofia are unincorporated crossroads with no dedicated ZIP code of their own; mail there is typically routed through the nearest town’s post office.
Geography
Union County sits on the Great Plains at the edge of the Raton-Clayton volcanic field, a landscape of grassland mesas and extinct volcanic cones, including Capulin Volcano National Monument. Elevations run from around 4,200 feet along the Canadian River to over 8,700 feet at Sierra Grande, an isolated shield volcano near Des Moines. The Canadian and Dry Cimarron rivers drain the county.
Union County borders Colorado to the north, Oklahoma and Texas to the east, and within New Mexico it borders Harding County to the south, Quay County to the southeast, and Colfax County to the west.
Demographics
Union County had 4,079 residents at the 2020 census, virtually all of it rural. Clayton is by far the largest community; Des Moines is a distant second. Median household income in the county trails the New Mexico median of $62,268, reflecting an economy built on ranching rather than higher-wage sectors. Population density is about one person per square mile, among the lowest in the state.
Economy & Local Life
Cattle ranching is the backbone of Union County’s economy, supplemented by dryland and irrigated farming, wind-energy development on the high plains, and highway commerce through Clayton along US 87 and US 56/64. Clayton is the county’s trade, school and government center; the county fairgrounds and the annual Union County Fair are the community’s biggest local gathering.
History
Union County was created by the territorial legislature in 1893 and formally organized on January 1, 1894, formed from parts of Colfax, Mora and San Miguel counties. It took its name because local residents were united in wanting a new county of their own. The county was originally much larger; it lost land when Quay County was split off in 1903 and Harding County in 1920, and once counted more than 20,000 residents before Dust Bowl-era drought and depopulation of the 1930s reduced the plains population permanently.
Getting There
US Highway 87 runs northwest–southeast through Clayton toward Raton and the Texas Panhandle, and US 56/64 crosses east–west toward Oklahoma and Springer.
- Raton, NM — about 85 miles northwest
- Dalhart, TX — about 55 miles east
- Trinidad, CO — about 95 miles north
- Tucumcari, NM — about 100 miles south
The nearest commercial airport is Denver International Airport, roughly 220 miles north; Clayton Municipal Airpark serves general aviation.
Frequently Asked Questions
Where is Union County, New Mexico?
It is in the state’s northeastern corner, bordering Colorado, Oklahoma and Texas.
What is the population of Union County?
4,079 people at the 2020 census.
How big is Union County?
3,831 square miles (9,920 km2), one of New Mexico’s largest counties by area and its least densely populated.
What is the county seat of Union County?
Clayton is the county seat.
How many towns are in Union County?
One incorporated town (Clayton), three incorporated villages (Des Moines, Folsom, Grenville), and several small unincorporated communities.
What ZIP codes are in Union County?
88415 (Clayton), 88418 (Des Moines), 88419 (Folsom), 88424 (Grenville), 88414 (Capulin), 88422 (Gladstone), 88410 (Amistad) and 88436 (Sedan).
What is Union County known for?
Capulin Volcano National Monument, cattle ranching, and dinosaur-track fossil sites near Clayton Lake State Park.
More counties in this state: Towns and villages in New Mexico.