Gaithersburg is a city in Montgomery County, Maryland. As of 2005, the city had an estimated total population of 57,698, making it the third largest in the state behind Baltimore and Frederick. This city is located at 39°8' North, 77°13' West, to the northwest of Rockville, the county seat of Montgomery County. Gaithersburg was incorporated in 1878. Gaithersburg apartments for rent comparison page shows most up to date rent information on Gaithersburg apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.