Gaithersburg, officially the City of Gaithersburg, is a city in Montgomery County, Maryland. At the time of the 2010 U.S. Census, Gaithersburg had a population of 59,933. It is the fourth largest incorporated city in the state, behind Baltimore, Frederick, and Rockville. Gaithersburg was incorporated as a town in 1878 and as a city in 1968.