The St. Clair Tunnel is a National Historic landmark located between Port Huron, Michigan and Sarnia, Ontario, Canada. It is basically two full size rail tunnels, big enough to accommodate railroads. They became a part of the NHL registry for their groundbreaking architecture, especially the first tunnel which has been used from 1891-1995.

The 1891 St. Clair Tunnel proved to be an excellent innovation built by the St. Clair Tunnel Company. It used new techniques in excavating in a compressed air setting. It used the Beach tunneling shield, after its designer Alfred Beach, to remove the material that is on the way of the tunnel. The other tunnel built in the 1990s was more of a smoother operation and was renamed to Paul M. Tellier Tunnel in 2004.