The following highways are numbered 321:
Canada Nova Scotia Route 321 Saskatchewan Highway 321
China China National Highway 321
Costa Rica National Route 321
Cuba Cuatro Caminos–Arroyo de Agua Road (1–321) Las Minas–Comunidad Pedro Pi Road (2–321) Santa Clara–Caibarién Road (4–321)
Japan Japan National Route 321
United States U.S. Highway 321 Arkansas Highway 321 Arkansas Highway 321 Spur Florida State Road 321 Georgia State Route 321 (former) Kentucky Route 321 Louisiana Highway 321 Mississippi Highway 321 Nevada State Route 321 New Mexico State Road 321 New York: New York State Route 321 County Route 321 (Erie County, New York) North Carolina Highway 321 (former) Ohio State Route 321 Pennsylvania Route 321 Puerto Rico Highway 321 Tennessee State Route 321 Texas: Texas State Highway 321 Texas State Highway Loop 321 Farm to Market Road 321 Virginia State Route 321 Virginia State Route 321 (former) Wyoming Highway 321