West Middlesex is a borough along the Shenango River in southwestern Mercer County, Pennsylvania, United States.

[5] According to the United States Census Bureau, the borough has a total area of 0.9 square miles (2.3 km2).

Samuel Byers, Andrew Wylie, William Bell, Richard Vanfleet and several others arrived in the vicinity in the late 18th century.

In 1787, James Gibson received a plot of land west of the Shenango River for military services.

In 1818, Jacob's son William Edeburn built a log grist mill on part of the land.

James Gilkey, cultivator of the "Neshannock potatoes," surveyed the site and platted the town in 1836 on McConnell's land.

A store and a tavern were opened about the time the town was platted, and in 1840 the post office was established, with Robert Young as the first postmaster.

The town is presently represented by Republican Mike Kelly in the House of Representatives, and voted for GOP incumbent Donald Trump in the 2020 presidential election by a 30 percentage point margin as opposed to Democratic challenger Joe Biden.

[15] West Middlesex is the home of an eponymous airport, though it exclusively serves general aviation and has no regularly scheduled commercial flights.