The Kenosha and Rockford Railroad (originally the Kenosha, Rockford & Rock Island Railroad), running between its two namesake cities in Wisconsin and Illinois, started in 1861, but was largely abandoned by 1939. This railroad, known as the Kenosha Division, or "KD Line", was merged early on into the Chicago & North Western Railroad. The line split west towards Loves Park, IL, going through Argyle, Harlem (which had a depot), a rock quary and into Loves Park. There is another line that runs along the east side of the Rock River; the two may have joined together at some point.
There is virtually no trace of the line's right-of-way today. However, the ROW once traversed property that is now submerged beneath the surface of Pierce Lake, a man-made lake in Rock Cut State Park. It is reported that, in the 1970s, a faulty drain caused the lake to drain, thus exposing the railbed which was easily identified and photographed.
Thanks to Mark Atkinson for contributing information about this route.