Tunnel City is an unincorporated census-designated place in the town of Greenfield, in Monroe County, Wisconsin, United States, named for the train tunnel just to the west which was used by the Chicago and North Western Railway (trackage now abandoned west of the tunnel) and the Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road). The existing track is owned by the Canadian Pacific Railway, and carries the Amtrak Empire Builder passenger train, though rail traffic is dominated by freight.