Coffeen is located in south central Illinois in Montgomery County northeast of St Louis between Hillsboro and Vandalia along Highway 185 about one mile from the northern shores of Coffeen Lake. The lake is the centerpiece of Coffeen Lake SFWA which offers hunting, fishing, hiking and power boating to its visitors.
The population estimate for July 1, 1998 was 792, an increase of 56 since 1990.