NY 321 is predominantly a north–south highway; however, a portion of the route through the towns of Elbridge and Camillus follows an east–west alignment.

NY 321 begins at an intersection with US 20 (West Genesee Street) in the Onondaga County village of Skaneateles.

The highway intersects Forward Road (unsigned NY 931F) just inside the Camillus town line soon after the turn.

[3] Past Forward Road, NY 321 becomes concurrent with CR 66 as maintenance of the roadway shifts from the New York State Department of Transportation to Onondaga County.

The state designation comes to an end at NY 5 in the hamlet of Bennetts Corners west of the village of Camillus shortly after; however, CR 66 continues onward.

An extension of the road south into the town of Skaneateles to the village of the same name was constructed in late 1912 and early 1913 and added to the state highway system in September 1913.

This part of NY 321 overlapped CR 66, a highway that began at the junction of Forward and Bennetts Corners Roads and ended in the hamlet of Memphis, and thus became maintained by Onondaga County.