Created on March 2, 1831, from part of Mifflin County and named for the Juniata River. The Indian name Juniata is said to mean “people of the standing stone.” Mifflintown, the county seat, was laid out in 1791 and incorporated as a borough on March 6, 1833. It was named for Governor Thomas Mifflin.

    Squatters settled here and were evicted by the provincial government in 1750. After they returned, Indians raided them in 1755–1756. There was protection from Forts Bigham and Peterson, but the Indians captured Bigham. The Pennsylvania Canal was the backbone of the early economy beginning in 1826, followed by the Pennsylvania Railroad in the late 1840s. The canal closed about 1900, and the Tuscarora Valley Railroad closed in 1934. Small clothing manufacturing continues to the present, but kosher poultry production is the biggest industry. Juniata is the fourth largest poultry-producing county in the state. Farms cover 36.6 percent of the land.