Montgomery, the spread.

Carved from Philadelphia, 1784.

Named for Richard Montgomery, the Revolutionary War general killed at the Battle of Quebec in 1775, the county was carved from the upper half of Philadelphia County in 1784. Norristown — chosen as the county seat for its central position — has held that title for two hundred and forty years.

For most of the 1800s, Montgomery County was farmland and small mill towns along the Schuylkill, Wissahickon, and Perkiomen creeks. Norristown grew on iron and railroad work. Conshohocken was Roberts' Iron Works. Pottstown built rolled steel. Ambler made asbestos products (the Keasbey & Mattison company defined the borough through the early 20th century). Each borough had a tight industrial economy and a tighter immigrant labor force — Welsh, German, then Italian, then African American, then Latin American as the decades moved.

The county's transformation was the postwar suburban build-out. Levittown's success in Bucks County lit up the same playbook here: farms became subdivisions, the Schuylkill Expressway opened in 1959, the Pennsylvania Turnpike's Northeast Extension opened in 1957, and by 1970 most of the original farms were gone. Lower Merion — already wealthy from its Main Line origin — became one of the densest concentrations of estate housing in the United States. Wissahickon, Upper Dublin, Methacton, and Lower Moreland filled in with family-anchor postwar housing. Pottstown and Norristown stayed working-class, then declined hard in the 1980s and 90s.

King of Prussia and the corporate ladder.

The single most important development in Montgomery County's last fifty years was the King of Prussia Mall and its surrounding corporate park. The mall opened in 1963 and is now the largest indoor shopping mall on the East Coast. The corporate park around it has accumulated headquarters and major operations for Comcast NBC, Lockheed Martin Space, GSK, Children's Hospital, AmerisourceBergen, Vertex Pharmaceuticals, and a half-dozen others. KOP is the largest concentration of corporate jobs in southeastern Pennsylvania outside Center City itself.

The result is a county whose price spread isn't an accident. Lower Merion estates and Conshohocken townhomes both serve KOP commuters. Wissahickon and Upper Dublin family singles serve dual-income corporate households. Pottstown and Norristown still have $200k starter homes that work for service-sector workers. There's a stratum here for every budget — and the right Montgomery County town is the one that matches your math.