county, central Pennsylvania, U.S., consisting of a mountainous area in the Appalachian Ridge and Valley physiographic province located midway between State College and Harrisburg. The county lies between Blue, Blacklog, and Shade mountains on the northwest and Tuscarora Mountain on the southeast. The principal waterways are the Juniata and Susquehanna (Susquehanna River) rivers and Blacklog, Tuscarora, East Licking, Lost, and West Branch Mahantango creeks. The Pennsylvania Canal became important to the region's development in the 1830s. The county was created in 1831; its name was derived from an Iroquoian Indian word meaning “people of the standing rock.”

The main boroughs are Port Royal, Mifflin, Thompsontown, and Mifflintown, which is the county seat. Agriculture (poultry and fruit) and manufacturing (textiles and wood products) form its economic base. Juniata county is one of seven completely rural counties in Pennsylvania. Area 392 square miles (1,014 square km). Pop. (2000) 22,821; (2007 est.) 23,168.