Montgomery County, locally also referred to as Montco, is the third-most populous county in the U.S. state and Commonwealth of Pennsylvania, and the 71st most populous in the United States. As of 2017, the census-estimated population of the county was 826,075, representing a 3.3% increase from the 799,884 residents enumerated in the 2010 census. Montgomery County is located adjacent to and northwest of Philadelphia. The county seat is Norristown. Montgomery County is geographically diverse, ranging from farms and open land in the extreme north of the county to densely populated suburban neighborhoods in the southern and central portions of the county.