This is the former Chicago Great Western railroad bridge over the Fox River, in St. Charles, Illinois. Originally part of CGW's mainline to Oelwein, Iowa, this line became a secondary route after the CGW was bought by the Chicago and North Western (another classic Midwestern road), which gradually cut the line shorter and shorter. Latterly part of the Union Pacific system, this line ended a few miles west of the bridge, dead ending just before a highway crossing. Today it's unused, the last customer on that side of the Fox having closed in 2009, and today the rails are cut off from the rest of the system by road construction on Route 64, which tore up the tracks at the grade crossing and which have not been reinstated.
Abandoned in place, the bridge and the tracks that are still there are some of the few remaining CGW structures in the area, which includes a few repurposed stations to the east and another bridge further west. One of the biggest legacies of the CGW is the Great Western Trail, a bike path that uses the former right of way, including that westernmost bridge in Elburn.