Worthington is a borough in Armstrong County, Pennsylvania, United States. The population was 639 at the 2010 census.
Worthington was laid out on a tract of land called Mt. Lorenzo by Judge James Barr in 1843–1844. He chose the location due to the nearby junction of two important early stage coach routes, the east–west route from Indiana, Pennsylvania, to Butler, and the north–south route from Freeport to Emlenton. It was incorporated as a borough in 1855. As the village grew into a town it variously relied upon farming and light manufacturing for its income. During the 1970s most manufacturing ceased. Agriculture is still important to the region, and a few light tool and die firms survive. The region also features coal, natural gas, and mineral extraction. In the 19th century an iron furnace and woolen mill were the main industrial operations, both owned and operated by Peter Graff I.
The town's first settlers were a mix of eastern Pennsylvanians and newly arrived immigrants of Scotch-Irish, German and English background.