The Borough of Thornburg, Pennsylvania, was originally founded in 1899 when cousins, Frank and David Thornburg formed a company to develop 250 acres into a suburban community. Thornburg was incorporated as a Borough in June 1909, from Robinson Township. The Thornburg School was constructed in 1910 and educated the children of the Borough until 1971, when Thornburg joined the Montour School District. The playground and tennis courts were added in 1939. The beautiful green space and park at the foot of town was first laid out as a golf course in 1898 and was one of the first in Allegheny County. By 1908, a clubhouse had been added, serving as a social center for the neighborhood. Members cut the grass on Saturdays and played golf on Sundays. The land was then privately owned for many years. In the spirit of "faith can move mountains", in December of 2005, Thornburg acquired the golf course property. This initiative began as a grass roots committee effort, gathering support throughout the community. Acquisition of the golf course was a result of fundraising, including private and government grants, and most importantly the overwhelming support and generosity of past and current residents. The "golf course" is now a conservation area to be enjoyed by present and future generations of Thornburgers. It provides a popular walking trail for people in the area.

Thornburg has always been a friendly, family centered town with a vibrant community spirit. The Thornburg Village Players, founded in 1938 continue to keep community theater alive, enjoyed by cast members and audiences alike. The Thornburg Community Club, founded in 1930 remains busy year round with children’s programs and activities, adult education, civic and social events. Whatever your interests, from yoga to international cuisine, from ballroom dance to gardening, from hiking to discussing a good book, Thornburgers have or will gladly embark on an activity that interests or inspires you. You are sure to have some good neighbors eager to join in the fun. It has often been said that you’ll never be without a fourth for bridge or tennis in Thornburg. We encourage you to experience "Pennsylvania’s best little borough" and make your own contribution to the history of Thornburg.

Thornburg has borders with Robinson Township to the north and west and Rosslyn Farms to the southwest. Across Chartiers Creek to the south and east, Thornburg runs adjacent with Crafton.