Montgomery County, PA has a population of 821, 725 people with a median age of 41. 4 and a median household income of 84, 113. Between 2015 and 2016 the population of Montgomery County, PA grew from 819, 264 to 821, 725, a 0. 3 increase and its median household income grew from 83, 254 to 84, 113, a 1. 03 increase.