Montgomery County, locally also referred to as Montco, is a county located in the Commonwealth of Pennsylvania. As of the 2010 census, the population was 799,874, making it the third-most populous county in Pennsylvania, after Philadelphia and Allegheny Counties, and the 71st most populous in the United States. The county seat is Norristown. Montgomery County is very diverse, ranging from farms and open land in Upper Hanover to densely populated rowhouse streets in Cheltenham.