Irwin, Pennsylvania is a borough located in Westmoreland County, Pennsylvania. It is situated approximately 25 miles east of Pittsburgh and is part of the Pittsburgh metropolitan area. The population was 2,631 at the 2010 census.

The town was founded in 1788 by John Irwin, a Revolutionary War veteran who purchased the land from the local Native American tribes. The town was originally called Irwin's Town but was later changed to Irwin Borough in 1872.

The town has a rich history and is home to many historical sites including the Old Stone House, which dates back to 1790 and is one of the oldest buildings in Westmoreland County. Other historic sites include the Irwin Railroad Station, which served as a stop on the Pennsylvania Railroad line from 1871 until it closed in 1971; and the Irwin Post Office, which opened in 1876 and still serves as an active post office today.

Irwin has several parks and recreational areas including Memorial Park, which features a playground, basketball court, tennis courts, baseball fields, and picnic pavilions; and Blythedale Park which offers walking trails and fishing ponds. The town also has several restaurants and shops located along Main Street.

Irwin is served by two school districts: Norwin School District for grades K-12; and Penn Trafford School District for grades 9-12. The town also has several churches including St. Paul's Lutheran Church (founded in 1790), St. John's United Church of Christ (founded in 1845), First Presbyterian Church (founded in 1848), Trinity United Methodist Church (founded in 1851), St. Mary's Roman Catholic Church (founded in 1870), and First Baptist Church (founded in 1895).