Mill Run is an unincorporated community and census-designated place (CDP) in Blair County, Pennsylvania, United States. It was first listed as a CDP prior to the 2020 census.

The CDP is in western Blair County, south of the center of Logan Township. It is bordered to the east by the city of Altoona and is often considered a neighborhood of the city. The community is in the valley of Mill Run, a stream which comes off the Allegheny Front 2 miles (3 km) to the west and flows southeast, then south, to join Beaverdam Creek west of Hollidaysburg. Allegheny Reservoir is just west of the CDP, and Mill Run Reservoir is 1 mile (1.6 km) upstream. Mill Run is part of the watershed of the Frankstown Branch Juniata River, leading to the Susquehanna.

Demographics

Historical population

Census	Pop.	Note	%±
2020	231		—
U.S. Decennial Census