List of highways numbered 421

Canada

• Manitoba [Provincial Road 421]
• Newfoundland and Labrador Route 421

Japan

• Japan [National Route 421]

United States

• U.S. Route 421
• Florida [State Road 421]
• * County Road 421 (Volusia County, Florida)
• Georgia [State Route 421]
• 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]