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 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.
The area was part of the original agricultural expansion after the initial settling of the first Maryland Colony in St. Mary's City, Maryland, which is several miles South of Great Mills. Early planters established farms in the area by the mid to late
A secret pony express is suspected by historians to
have run through Great Mills at night for over a year, carrying military intelligence messages from a clandestine citizen militia base in Point Lookout, Maryland. The pony express carried messages all the way to Washington D. C. (possibly passing through
the Great Mills area), keeping the President of the United States informed of British Naval movements on the Chesapeake Bay. The British finally came ashore in Point Lookout, seizing the area and putting a stop to the operation.
Two Medal of Honor winners hail from Great Mills. William H. Barnes
and James H. Harris were both free African-American farmers who grew up in Great Mills and served as soldiers in the Union Army during the American Civil War. They are both specifically mentioned and memorialized (including being discussed and depicted
in a special permanent display) at the United States Colored Troops Memorial Statue which is just North of Great Mills in Lexington Park, Maryland. The site is also a memorial to the more than 700 African-American soldiers and sailors from St. Mary's
County, Maryland who served in the Union forces during the American Civil War (this is also discussed in the educational display). Special celebrations are also held there each year.