Alamosa County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 16,376. The county seat is Alamosa. The county name is the Spanish language word for a grove of cottonwood trees.

Alamosa is a home rule municipality and the county seat of Alamosa County, Colorado, United States. The city population was 9,806 in the 2020 United States Census. The city is the commercial center of the San Luis Valley in south-central Colorado, and is the home of Adams State University.