Route 921 provides local circulator service in Herndon. The route travels primarily along the Worldgate Drive and Elden Street corridors.

This route serves the north side of the Herndon Metro Station at a bus stop located on Herndon Parkway.

Popular locations along the route include:

• Worldgate Centre
• Herndon Marketplace
• Elden Street Marketplace
• Herndon Middle School
• Herndon Post Office