Great Mills is an unincorporated community in St. Mary's County, Maryland, United States. Great Mills High School serves the lower end of the county, including the town (census CDP) of Lexington Park.
The area is site of some of the oldest agricultural settlements in Maryland, as well as English speaking North America. It had many links to the original Maryland colony in St. Mary's City, Maryland.
It is also now a suburb of Lexington Park, Maryland and the Patuxent River Naval Air Station.