Gaithersburg , officially the City of Gaithersburg, is a city located in Montgomery County, Maryland. At the time of the 2010 census, Gaithersburg had a population of 59,933, making it the fourth largest incorporated city in the state, behind Baltimore, Frederick, and Rockville. Gaithersburg is located to the northwest of Washington, D.C., and is considered a suburb and a primary city within the Washington–Arlington–Alexandria, DC–VA–MD–WV Metropolitan Statistical Area. Gaithersburg was incorporated as a city in 1878.