Big Run is a borough in Jefferson County, Pennsylvania, United States.

[4] Big Run is located in southeastern Jefferson County at 40°58′12″N 78°52′40″W / 40.97000°N 78.87778°W / 40.97000; -78.87778 (40.969945, -78.877848),[5] on the north side of Mahoning Creek, a westward-flowing tributary of the Allegheny River.

The borough is named for Big Run, which joins Mahoning Creek at the western end of the community.

[3] As of the census[7] of 2000, there were 686 people, 282 households, and 194 families residing in the borough.

26.2% of all households were made up of individuals, and 11.0% had someone living alone who was 65 years of age or older.