In 1874, the Fond du Lac, Amboy & Peoria Railway intended to build a 3' narrow-gauge railroad from Fond du Lac southwards to Amboy, IL, in order to access both the lumber of central WI and the the coal fields of central IL. After some political obstacles, construction of the line began in 1876, with the line reaching as far south as Iron Ridge, WI by 1877. However, upon connecting with the standard-gauage Chicago, Milwaukee & St. Paul Railroad (precursor to the Milwaukee Road) at Iron Ridge Junction, construction ceased, leaving only 29 miles of track laid. The entire route was purchased by the CM&StP in 1883 and consequently converted to standard-gauge soon after.
The line served many iron mines and quarries along its route, including the Northwestern Iron Company in Mayville, WI.
Fond du Lac, WI, was a very busy rail hub with Milwaukee Road running to the southwest to Horicon, Soo Line to the southwest to Waukesha and northwest to Stevens Point, plus Chicago North Western had lines from Sheboygan to the east, Milwaukee to the southeast, Janesville to the southwest, Wisconsin Rapids to the west-northwest and Green Bay to the north. All of this in addition to very busy rail yards for both CNW and Soo Line. The yards are still pretty busy as are the repair facilities but the only lines that are still active are the former Soo Line to the southwest and the CNW north.
The line was abandoned between Fond du Lac and Mayville in the early 1980s. The section between Mayville and Iron Ridge Junction is still in use by the Wisconsin & Southern Railroad.