Mount Rainier /reɪˈnɪər/ is a city in Prince George's County, Maryland, United States. The population was 8,080 at the 2010 census. Bordering Washington, D.C., Mount Rainier got its start as a streetcar suburb. (See Streetcars in Washington, D.C.) According to local tradition, surveyors from the Pacific Northwest named the town, giving the streets names such as "Shasta" and "Cascade". Historic U.S.