Summerfield is a village in St. Clair County, Illinois, United States. The population was 451 at the 2010 census. Summerfield is located at 38°35′49″N 89°45′4″W / 38.59694°N 89.75111°W. According to the 2010 census, Summerfield has a total area of 0.431 square miles, of which 0.43 square miles is land and 0.001 square miles is water.