Altona is a census-designated place (CDP) in Boulder County, Colorado, United States. As of the 2010 census it had a population of 501.
Altona is located in central Boulder County at 40°7′21″N 105°17′46″W / 40.12250°N 105.29611°W (40.1225330, -105.2960570), where Left Hand Creek exits the Front Range of the Colorado Rockies. U.S. Highway 36 passes through the community, leading north to Lyons and south to Boulder. Altona is 10 miles (16 km) west of Longmont by Nelson Road.
According to the U.S. Census Bureau, the Altona CDP has a total area of 1.7 square miles (4.5 km2), of which 1.7 square miles (4.4 km2) is land and 0.039 square miles (0.1 km2), or 3.31%, is water.