Armstrong County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 65,558. The county seat is Kittanning. The county was organized on March 12, 1800, from parts of Allegheny, Westmoreland and Lycoming Counties. It was named in honor of John Armstrong, who represented Pennsylvania in the Continental Congress and served as a major general during the Revolutionary War.

Kittanning is a borough in and the county seat of Armstrong County, Pennsylvania, United States. It is situated 36 miles (58 km) northeast of Pittsburgh, along the east bank of the Allegheny River. The population was 3,921 at the 2020 census.