Rosaryville is an unincorporated area and census-designated place (CDP) in Prince George's County, Maryland, United States, located south of Cinton and Upper Marlboro beside U.S. Route 301. Per the 2020 census, the population was 11,548. including housing developments and rural open space. It was named for a local Roman Catholic church. Close to Rosaryville are the Marlton housing development, Maryland Veterans Cemetery, the Southern Maryland Farmers Market, and Rosaryville State Park.