Where Is San Juan County? All 4 San Juan Counties on a Map

Where is San Juan County?

4 San Juan Counties in 4 states · 154,272 people (2025)

There are 4 counties named San Juan County in the United States, in Colorado, New Mexico, Utah and Washington. The most populous is San Juan County, New Mexico (county seat: Aztec), with 120,340 people in 2025. 2 of them are named after San Juan River, tributary of the Colorado River in Utah, Colorado, and New Mexico in the United States.

All 4 San Juan Counties

Sorted by state. Each link opens the county's map.

State	County seat	Population 2025	Land area (sq mi)	Established	Named after
San Juan County, Colorado	Silverton	813	388	1876	John the Apostle
San Juan County, New Mexico	Aztec	120,340	5,517	1887	San Juan River
San Juan County, Utah	Monticello	14,542	7,824	1880	San Juan River
San Juan County, Washington	Friday Harbor	18,577	174	1873	San Juan Islands

Questions about San Juan Counties

How many San Juan Counties are there?

There are 4 San Juan Counties in the United States, in Colorado, New Mexico, Utah and Washington.

Which San Juan County is the largest?

By population, San Juan County, New Mexico (120,340 people in 2025). By land area, San Juan County, Utah (7,824 sq mi).

Which San Juan County is the oldest?

San Juan County, Washington, established in 1873. The newest is San Juan County, New Mexico (1887).

Why are there so many San Juan Counties?

2 of the 4 are named after San Juan River, tributary of the Colorado River in Utah, Colorado, and New Mexico in the United States. Many counties took their names from the same founders, presidents and generals as new states were organized.

How do I find out which San Juan County an address is in?

Open the county map of the state: it has a search box for cities, towns and ZIP codes. On a phone, the "what county am I in" tool on our sister site uses your location.

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