Dahlgren is a village in Hamilton County, Illinois, United States. The population was 514 at the 2000 census. It is part of the Mount Vernon Micropolitan Statistical Area.
Dahlgren is located at 38°11′57″N 88°41′9″W / 38.19917°N 88.68583°W / 38.19917; -88.68583 (38.199117, -88.685737). The mean elevation of the village is 155.5 meters (510 ft).
According to the United States Census Bureau, the village has a total area of 1.0 square miles (2.6 km²), all of it land.