The following highways are numbered 421:
Canada
- Manitoba Provincial Road 421
- Newfoundland and Labrador Route 421
Japan
Japan National Route 421
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United States
U.S. Route 421
Florida State Road 421 
County Road 421 (Volusia County, Florida)
Georgia State Route 421 (unsigned designation for Interstate 516)
New Mexico State Road 421
New York State Route 421
Ohio State Route 421
Puerto Rico Highway 421
South Carolina Highway 421
Tennessee State Route 421
Texas State Highway Spur 421
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| Previous | Lists of highways | Next |
|---|---|---|
| 420 | 421 | 422 |