San Acacio is an unincorporated community and a census-designated place (CDP) located in and governed by Costilla County, Colorado, United States.

The population of the San Acacio CDP was 56 at the 2020 United States census.

[3] The Sanford post office (Zip Code 81151) serves San Acacio postal addresses.

[4] San Acacio is located in the Rio Culebra valley of the Sangre de Cristo Land Grant which was awarded to the family of Carlos Beaubien in 1843.

Colorado State Highway 142 runs through San Acacio, leading east 8 miles (13 km) to San Luis and west 25 miles (40 km) to U.S. Route 285 at Romeo.