Mount Rainier is a city in Prince George's County, Maryland, United States, bordering Washington D.C. The population was 8,333 at the 2020 census. Mount Rainier is contained between the Northwest Branch Anacostia River, Cedar Lane Alley, and 34th Street to the north, 37th Street and 37th Place to the northeast, Upshur Street and Queens Chapel Road to the west, the CSX Capital Subdivision train tracks to the east, and Eastern Avenue NE to the south. Mount Rainier got its start as a streetcar suburb, when tracks were laid for the 82 Streetcar Line. According to local tradition, surveyors from the Pacific Northwest named the town, giving the streets names such as Shasta and Cascade. Historic U.S. 1 runs through the center of the town and serves as the main street and central business district.

Prince George's County is located in the U.S. state of Maryland bordering the eastern portion of Washington, D.C. As of the 2020 U.S. census, the population was 967,201, making it the second-most populous county in Maryland, behind neighboring Montgomery County. The 2020 census counted an increase of nearly 104,000 in the previous ten years. Its county seat is Upper Marlboro. It is the largest and the second most affluent African American-majority county in the United States, with five of its communities identified in a 2015 top ten list.