Pennsylvania Route 850 is a 44-mile-long (71 km) state highway located in Juniata and Perry counties in Pennsylvania. The western terminus is at PA 35 in Tuscarora Township. The eastern terminus is at U.S. Route 11 /US 15 in Marysville. PA 850 is a two-lane undivided road that runs through rural areas in the Ridge-and-Valley Appalachians. The route heads southeast from PA 35 and crosses PA 75 in Honey Grove before it traverses Tuscarora Mountain and leaves Juniata County for Perry County. PA 850 continues southeast and crosses PA 17 in Kistler before running east concurrent with PA 274 between Fort Robinson and Loysville. The route turns back to the southeast and heads south concurrent with PA 233 into Landisburg. PA 850 heads east, crossing PA 74 in Alinda before following PA 34 southeast between Dromgold and Shermans Dale. From here, the route continues east to its terminus in Marysville. PA 850 was designated in 1928 to run from PA 274 in Fort Robinson northwest to Kistler, with the road between Landisburg and Dromgold designated as part of PA 233. In 1937, the route was extended to its current length between PA 35 in Tuscarora Township and PA 14 in Marysville, replacing the portion of PA 233 between Landisburg and Dromgold.

Juniata County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 23,509. Its county seat is Mifflintown. The county was created on March 2, 1831, from part of Mifflin County and named for the Juniata River. The county is part of the Central Pennsylvania region of the state.