County · code 35059
Union CountyNew Mexico
Union County is a county in New Mexico with its seat in Clayton. It was created on January 1, 1894, from Colfax, Mora, and San Miguel counties.
- Founded1894
- County seatClayton
- Land area3,825 sq mi + 6 sq mi water
- Population4,079 2020 Census
Where it is
Union on the map of New Mexico
New Mexico has 33 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Formed in 1894 from Colfax County, Mora County and San Miguel County
An old deed may name a county that no longer exists, or a boundary that has since moved.
Union County was created by New Mexico Territory from Colfax, Mora, and San Miguel counties when an act passed on February 23, 1893, and took effect on January 1, 1894. In 1903 and 1907, Union County lost territory to the creation and establishment of Quay County. The county lost additional territory to the creation of Harding County on June 10, 1921.
- 1894Union County created Union created by New Mexico Territory from Colfax, Mora, and San Miguel. Act passed 23 February 1893; took effect 1 January 1894. · N.M. Terr. Laws 1893, 30th assy., ch. 49/pp. 68-75
- 1895Boundary clarified Union boundary was clarified to correct an "uncertainty, ambiguity and apparent contradiction in the language" of the 1 January 1894 law (no change).no change· N.M. Terr. Laws 1895, 31st assy., ch. 12/p. 43
- 1903Lost territory Union lost to creation of Quay. · N.M. Terr. Laws 1903, 35th assy., ch. 8/pp. 16-20
- 1907
- 1921Lost territory Union lost to creation of Harding. · N.M. Laws 1921, 5th reg. sess., ch. 48/pp. 106-107
Land and parcels
What the maps cover in Union
Who publishes each layer, how good it is, and when we last checked.
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Parcels Missing
No public parcel map found for Union County yet. Lot lines and owners of record are kept by the county (unionnm.us).
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Address points Missing
No public address points layer found for Union County yet.
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Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
Union by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
Union County's official site
We have found the county's site but not its offices yet; start there.
County government
- County government
The official website of Union County.
See your own lot on these maps
Open Union County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about Union County
- When was Union County founded?
- Union County was founded in 1894, formed from Colfax County, Mora County and San Miguel County.
- What is the county seat of Union County?
- The county seat of Union County is Clayton.
- Is there an online parcel map for Union County?
- Not that we have found yet. Lot lines and owners of record are kept by the county assessor's office. When a public parcel map appears, it shows here.
- Has Union County's boundary or name changed?
- Union County was created in 1894 from Colfax County, Mora County and San Miguel County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Quay County and Harding County.
- Is my lot in a flood zone?
- We do not have flood maps for Union County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby