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
• 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