Montgomery County, officially the County of Montgomery, is a county in the U.S. state of Maryland. It is the largest county in the state of Maryland, located adjacent to Washington, D.C. It includes Bethesda, Chevy Chase, Potomac, Silver Spring, Rockville, Kensington, Wheaton, Gaithersburg, Germantown, Derwood, Olney, Montgomery Village, Clarksburg, Dickerson, Poolesville, and more. Montgomery County MD real estate market is the most expensive and hottest in Maryland.