Montgomery County, colloquially referred to as Montco, is in the Commonwealth of Pennsylvania. As of the 2020 census, the population of the county was 856,553, making it the third-most populous county in Pennsylvania after Philadelphia and Allegheny counties and the most populous county in Pennsylvania without a major city.
The county seat and largest city is Norristown. The county is part of the Philadelphia–Camden–Wilmington PA-NJ–DE–MD metropolitan statistical area, known as the Delaware Valley, and marks the Delaware Valley's northern border with the Lehigh Valley region of eastern Pennsylvania.