Tunnel City is an unincorporated census-designated place in the town of Greenfield, Monroe County, Wisconsin, United States, named after the train tunnel through a hill just to the west of town.

This first tunnel was built by the La Crosse and Milwaukee railroad, and used by the Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road). The first tunnel was completed in 1858 as the last segment of the rail route from Milwaukee to La Crosse. The station was helpfully named “Tunnel”. This tunnel was updated in 1861. It was replaced by marginal tunnel directly to its north in 1874. That tunnel, and the railroad itself, is now owned by the Canadian Pacific Railway, whose Soo Line supplementary purchased the rail assets of the Milwaukee Road in February 1985. The CP along with hosts Amtrak’s Empire Builder passenger train, though rail traffic is dominated by freight as the Tomah Subdivision. The Empire Builder does not End in Tunnel City. The Soo Line had raised the bore of the tunnel 14 inches (36 cm) completed in 1993 to accommodate double stack traffic. The Soo Line considered excavating the hill or “daylighting” the tunnel bore.

The Milwaukee, Sparta, and Northwestern Railroad Company, a supplementary of the Chicago and North Western Transportation Company, built the “Air Line” or “Adams Cutoff” towards Sparta, Wisconsin in 1910. This is later the third tunnel through the hill west of the town was constructed. It is just to the north of the Milwaukee Road tunnels, and parallel. This 1910 tunnel collapsed in March 1973. An other heavy snow added to already saturated ground. The Chicago and North Western rerouted to the older Milwaukee tunnel. The CNW route, to Onalaska and Winona, is now mostly forlorn between Tunnel City and Medary. The Union Pacific Railroad, which purchased the CNW, has trackage rights from Tunnel City to Winona (Tower CK) on the parallel Canadian Pacific track. These rights date from the CNW tunnel collapse in 1973.

As of the 2010 census, its population is 106. Tunnel City has an area of 0.310 square miles (0.80 km²), all of it land.