Costilla County area

Population and density of Costilla County

The Census Bureau estimates that 3,679 people lived in Costilla County on July 1, 2025. That ranks #2,986 of 3,222 county equivalents nationally and #55 of 64 in Colorado. Since the April 1, 2020 estimates base of 3,494, the population has grown by 185 (+5.3%), compared with +4.1% for Colorado as a whole.

With 1,227.6 square miles of land, that is 3 people per square mile (1.2 per km²), placing Costilla County #2,984 nationally for density and #51 in Colorado. The median county equivalent has 47 people per square mile; the Colorado median is 11. Put another way, there are about 214 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Costilla County

2 incorporated places lie at least partly in Costilla County. Together they are home to 917 people (24.9%); the other 2,762 (75.1%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is San Luis town, with 597 residents in the county. By land, Blanca town is the largest at 1.833 mi².

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Costilla County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Costilla County is an outlying county of the Alamosa, CO Micropolitan Statistical Area. Its 3 county equivalents have 27,896 residents on 3,237.7 square miles of land; Costilla County accounts for 37.9% of the land and 13.2% of the residents. By combined land it ranks #44 of 542 micropolitan areas, and #456 by population.

ZIP codes

7 ZIP Code Tabulation Areas have land in Costilla County; 6 of them have most of their land inside the county, and the others mainly cover neighboring areas.

81055811238112681133811388115181152

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Costilla County

Costilla County shares a land border with 6 county equivalents, including 2 in New Mexico. It has more land than 1 of them. The largest neighbor is Las Animas County (4,772.9 mi²) and the smallest is Alamosa County (722.6 mi²). Together with its neighbors, Costilla County forms a block of 15,562 mi² of land, of which it holds 7.9%.

How big is Costilla County compared with U.S. states?

Costilla County has more land than 1 of the 50 states. It is about 1.2 times the land area of Rhode Island (1,033.9 mi²), while Delaware, the next larger state, has 1.6 times as much land (1,948.6 mi²). Colorado’s county land could hold about 84 areas the size of Costilla County.

Another way to picture it: the same land area would fill a square about 35 miles (56.4 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Costilla County?

Costilla County has more land than 2,722 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Costilla County at #574 nationally by total area, 74 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 0.3%, compared with a national county-equivalent median of 1.2% — 0.9 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Costilla County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.