The following highways are numbered 123:

Australia

- Now Newcastle Inner City Bypass

Brazil

• SP-123 (Rodovia Floriano Rodrigues Pinheiro)

Canada

• New Brunswick Route 123
• Ontario Highway 123 (former)
• Prince Edward Island Route 123
• Saskatchewan Highway 123

Costa Rica

• National Route 123

India

• National Highway 123 (India) (NH 123) in the states of Rajasthan and Uttar Pradesh

Japan

• Japan National Route 123

Malaysia

• Malaysia Federal Route 123 (Jalan Rasau Kerteh Selatan), Terengganu, Malaysia

Mexico

• Mexican Federal Highway 123 (Carretera Federal 123)

Spain

• N-123 road (Spain)

United States

• U.S. Route 123
  • U.S. Route 123 (Kentucky) (former)
• Alabama State Route 123
• Arkansas Highway 123
• California State Route 123
• Connecticut Route 123
• Florida State Road 123
  • County Road 123 (Baker County, Florida)
• Georgia State Route 123
• Hawaii Route 123 (former)
• Illinois Route 123
• Indiana State Road 123 (former)
• Iowa Highway 123 (former)
• K-123 (Kansas highway)
• Kentucky Route 123
• Louisiana Highway 123
• Maine State Route 123
• Maryland Route 123 (former)
• Massachusetts Route 123
• M-123 (Michigan highway)
• Minnesota State Highway 123
• Missouri Route 123
• New Hampshire Route 123
  • New Hampshire Route 123A
• County Route 123 (Bergen County, New Jersey)
• New York State Route 123
  • County Route 123 (Jefferson County, New York)
  • County Route 123 (Niagara County, New York)
• North Carolina Highway 123
• Ohio State Route 123
• Oklahoma State Highway 123
• Pennsylvania Route 123 (former)
• Rhode Island Route 123
• South Dakota Highway 123
• Tennessee State Route 123
• Texas State Highway 123
  • Texas State Highway Loop 123
  • Farm to Market Road 123
• Utah State Route 123
• Vermont Route 123
• Virginia State Route 123
  • Virginia State Route 123 (1923-1928) (former)
  • Virginia State Route 123 (1928-1933) (former)
  • Virginia State Route 123 (1933-1940) (former)
• Washington State Route 123
• West Virginia Route 123
• Wisconsin Highway 123

Territories

• Puerto Rico Highway 123