Montgomery County, colloquially referred to as Montco,^[1] is a county 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.^[2] The county is part of the Southeast Pennsylvania region of the state.^{[lower-alpha 1]}

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Montgomery County
County
Montgomery County Courthouse in Norristown, May 2007
Flag Seal
Nickname:  Montco[1]
Location within the U.S. state of Pennsylvania
Pennsylvania's location within the U.S.
Coordinates: 40°13′N 75°22′W
Country	United States
State	Pennsylvania
Founded	September 10, 1784
Named for	Richard Montgomery or Montgomeryshire
Seat	Norristown
Largest municipality	Lower Merion Township
Government
• County Commissioners	Jamila H. Winder, Chair Neil K. Makhija, Vice Chair Thomas DiBello, Commissioner
Area
• Total	487 sq mi (1,260 km2)
• Land	483 sq mi (1,250 km2)
• Water	4.2 sq mi (11 km2)  0.9%
Population  (2020)
• Total	856,553
• Estimate  (2022)	864,683
• Density	1,773/sq mi (685/km2)
Time zone	UTC−5 (Eastern)
• Summer (DST)	UTC−4 (EDT)
Congressional districts	1st, 4th, 5th
Website	www.montcopa.org

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The county seat and largest city is Norristown.^[3] 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.

The county borders Philadelphia, the nation's sixth-largest city, to its southeast, Bucks County to its east, Berks and Lehigh counties to its north, Delaware County to its south, and Chester County to its southwest.

The county was created on September 10, 1784, out of land originally part of Philadelphia County. The first courthouse was housed in the Barley Sheaf Inn. It is believed to have been named either for Richard Montgomery, an American Revolutionary War general killed in 1775 while attempting to capture Quebec City, or for the Welsh county of Montgomeryshire, which was named after one of William the Conqueror's main counselors, Roger de Montgomerie, since it was part of the Welsh Tract, an area of Pennsylvania settled by Quakers from Wales.^[4]

According to the U.S. Census Bureau, the county has a total area of 487 square miles (1,260 km²), 483 square miles (1,250 km²) of which was land and 4.2 square miles (11 km²) (0.9%) of which was water.^[5]

Montgomery County is a suburb of Philadelphia, the nation's sixth most populous city. Many Montco residents work in the city, but the county is also a major employment center with large business parks in Blue Bell, Lansdale, Fort Washington, Horsham, and King of Prussia attracting thousands of workers from all over the region. The strong job base and taxes generated by those jobs have resulted in Montgomery County receiving the highest credit rating of 'AAA' from Standard & Poor's, one of fewer than 30 counties in the United States with such a rating.^[14] In 2012, Moody's downgraded the general obligation rating to Aa1,^[15] and in 2018 the rating was revised back to Aaa.^[16]

Major employers include:^[17]

Under Pennsylvania law, five types of incorporated municipalities are listed: cities, boroughs, townships, home rule municipalities (which can include communities that bear the name "Borough" or "Township") and, in at most two cases, towns. These boroughs, townships, and home rule municipalities are located in Montgomery County:

• The Institutes for the Achievement of Human Potential (IAHP), a nonprofit organization founded by Glenn Doman, was established in Wyndmoor in 1955. The IAHP is an educational organization that teaches parents about child brain development, and is a treatment center for brain-injured children.
• The Old York Road Symphony, based in Abington, is one of the oldest all-volunteer orchestras in the country, founded in 1932.

The majority of the county has a hot-summer humid continental climate (Dfa). In most southern areas of the county and along the Schuylkill River including Pottstown a humid subtropical climate (Cfa) exists. The hardiness zone is 7a for the majority of the county and 7b in most areas south of Interstate 276. 6b only continues to exist in some very small higher areas in the north.

As of March 4, 2024, there are 606,385 registered voters in Montgomery County.^[25]

• Democratic: 302,985 (49.96%)
• Republican: 205,268 (33.85%)
• Independent: 67,703 (11.16%)
• Minor parties: 30,429 (5.02%)

Montgomery County historically was a stronghold for the Republican Party. The county was the only one carried by Barbara Hafer in the 1990 gubernatorial election over the incumbent governor, Bob Casey. However, the Democratic Party has made substantial gains in the county over the last quarter-century and gained the registration edge early in 2008.

Like neighboring Bucks County, the county voted Democratic during the Civil War era, voting Democratic between 1856 and 1876, except in 1860 and 1872. Like most of Philadelphia's suburbs, the brand of Republicanism practiced in Montgomery County for much of the 20th century was moderate. As the national parties have polarized, the county's voters have increasingly supported Democrats at the national level. The county voted for the Republican presidential nominee in all but two elections from 1880 to 1988, that being in 1892 and 1964. However, Montgomery County residents have voted for the Democratic presidential nominee since 1992, with the margins progressively increasing between every election, except in 2012. In the 2020 election, Joe Biden became the first Democrat to obtain over 60% of the county's vote.

Despite Donald Trump's victory in the state of Pennsylvania in the 2016 presidential election, Montgomery County was one of the few counties in Pennsylvania that swung in the Democratic presidential candidates' direction with Hillary Clinton winning Montgomery County with 58.87% of the vote, an improvement from Barack Obama's 56.6% vote share in 2012. In the 2016 U.S. Senate and Pennsylvania Attorney General elections, Montgomery County voted for Katie McGinty and Josh Shapiro, both Democrats.^[26]

Most county-level offices were held by Republicans until after the 2007 election, when Democrats picked up control of five row offices. Democrats have also won several elections in the Pennsylvania General Assembly in recent years, including two GOP-leaning State House districts in 2004, the 148th with Mike Gerber and the 153rd with current Governor Josh Shapiro. Today, although the county is very Democratic at the national level, at the state and local level, it is not specifically partisan.

In the 2004 United States Senate election, Republican Arlen Specter won the county over Montco resident Joe Hoeffel, but Democrat Bob Casey, Jr. out-polled Rick Santorum in the 2006 Senate election. In 2006, Democrat Rick Taylor unseated incumbent Republican Eugene McGill in the 151st, although Taylor lost in 2010 to Republican Todd Stephens and, in 2008, Democrat Matthew Bradford unseated incumbent Republican Jay Moyer in the 70th. Six of the county's 12 state house seats and four of the county's eight senate seats are now held by Democrats. All four statewide Democratic candidates carried Montgomery in 2008, with Barack Obama receiving 60% of the county's vote. Barack Obama won Montgomery County in 2008 and 2012.

Montgomery County is governed by a three-person county commission. The current composition is two Democrats and one Republican. By law, the county commission must have one member of a minority party represented.

• National Register of Historic Places listings in Montgomery County, Pennsylvania