Pennsylvania Route 321 (PA 321) is a 43.8-mile-long (70.5 km) state highway located in Elk and McKean counties in the U.S. state of Pennsylvania, maintained by the Pennsylvania Department of Transportation (PennDOT). The southern terminus is at U.S. Route 219 (US 219) in the community of Wilcox. The northern terminus is at PA 346 within the Allegheny National Forest. PA 321 heads northwest from Wilcox through rural areas to the borough of Kane, where it forms a brief concurrency with US 6. North of here, the route heads through the national forest and runs along the shore of the Allegheny Reservoir. PA 321 runs east briefly with PA 59 before winding north through more forest to its northern terminus. A portion of the route along the Allegheny Reservoir is designated as the Longhouse National Scenic Byway, a Pennsylvania Scenic Byway and National Forest Scenic Byway. The road between Wilcox and Kane was designated as part of PA 6 in 1924. US 119 became concurrent with PA 6 in 1926 before US 219 replaced both designations on this stretch of road two years later. The road between Kane and Kinzua was built in the late 1920s and became an extension of PA 68 in 1935. In 1952, US 219 was relocated off the road between Wilcox and Kane. Plans were made to construct the Kinzua Dam in 1960, and several new roads would need to be built to accommodate the reservoir including a relocation of PA 68. In 1961, the PA 321 designation was approved for the unnumbered road between Wilcox and Kane and PA 68 between Kane and Kinzua in order to provide an access road to the planned recreation area; signs were posted the following year. The PA 321 designation north of Kane was removed in 1966. In the late 1960s, the section between 4 miles (6.4 km)^* north of Kane and PA 346 was constructed, including a new alignment between Red Bridge and PA 59. Work on the 4-mile (6.4 km) segment north of Kane took place in the early 1970s. In Kane, PA 321 was relocated from following US 6 through the downtown area to use Hacker Street to the east, with reconstruction finished in 1973. The road between Wilcox and Kane, including a bypass of the former, was rebuilt in the mid-1970s. In 1974, PA 321 was extended from US 6 in Kane north to PA 346.

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