Crestline is a village in Crawford and Richland Counties in the U.S. state of Ohio. The population was 4,630 at the 2010 census. It is the third largest municipality in Crawford County. The Crawford County portion of Crestline is part of the Bucyrus Micropolitan Statistical Area, while the small portion of the village that extends into Richland County is considered part of the Mansfield Metropolitan Statistical Area.