List of highways numbered 121

• Alabama State Route 121
• Arkansas Highway 121
• California State Route 121
• Colorado State Highway 121
• Connecticut Route 121
• County Road 121 (Duval County, Florida)
• County Road 121 (Hennepin County, Minnesota)
• County Road 121A (Alachua County, Florida)
• County Route 121 (Herkimer County, New York)
• County Route 121 (Jefferson County, New York)
• County Route 121 (Montgomery County, New York)
• County Route 121 (Niagara County, New York)
• County Route 121 (Seneca County, New York)
• County Route 121 (Steuben County, New York)
• County Route 121 (Sullivan County, New York)
• Farm to Market Road 121
• Florida State Road 121
• Georgia State Route 121
• Hawaii Route 121
• Illinois Route 121
• Indiana State Road 121
• Japan National Route 121
• K-121 (Kansas highway)
• Kentucky Route 121
• Louisiana Highway 121
• M-121 (Michigan highway)
• Maine State Route 121
• Maryland Route 121
• Massachusetts Route 121
• Minnesota State Highway 121
• Missouri Route 121
• National Route 121 (Costa Rica)
• Nebraska Highway 121
• Nevada State Route 121
• New Brunswick Route 121
• New Hampshire Route 121
• New Hampshire Route 121A
• New Mexico State Road 121
• New York State Route 121
• North Carolina Highway 121
• Ohio State Route 121
• Ontario Highway 121
• Pennsylvania Route 121
• Prince Edward Island Route 121
• Puerto Rico Highway 121
• Rhode Island Route 121
• South Carolina Highway 121
• Texas State Highway 121
• Texas State Highway Loop 121
• Texas State Highway Spur 121
• U.S. Route 121
• U.S. Route 121 (1926)
• Utah State Route 121
• Vermont Route 121
• Virginia State Route 121
• Virginia State Route 121 (1923-1926)
• Virginia State Route 121 (1927-1928)
• Virginia State Route 121 (1928-1933)
• Washington State Route 121
• Wisconsin Highway 121