The F40C is derived from the EMD SDP40F; the primary difference between the two is the substitution of a 500-kilowatt (670 hp) HEP generator for the SDP40F's steam generator. It is powered by a 16 cylinderEMD 645E3B, producing 3,200 horsepower (2,390 kW). It uses the same frame as the EMD SD40-2, giving it an overall length of 68 feet 10 inches (20.98 m).
In the early 1970s the Chicago, Milwaukee, St. Paul and Pacific Railroad ("Milwaukee Road") operated two commuter rail lines in Chicago: Chicago–Fox Lake and Chicago–Elgin. The operation of these lines was subsidized by local transit agencies. In 1974 two local agencies, the North West Suburban Mass Transit District and the North Suburban Mass Transit District, funded the acquisition of 15 F40Cs for use on the Milwaukee lines. The locomotives passed to Metra on the latter's creation in the 1980s but continued to operate on the ex-Milwaukee lines.
The F40C was withdrawn from regular service with the arrival of new MPI MP36PH-3S locomotives in 2003–2004. Thirteen locomotives were sold to locomotive leasing corporations, although units 611 and 614 were retained and kept on the property in the Western Avenuerailyard. In the spring of 2009, units 611 and 614 were placed back into revenue service on both of Metra's ex-Milwaukee Road commuter lines. This was done to cover schedules while the oldest units in Metra's EMD F40PH fleet were being rebuilt. Towards the end of 2016, with many F40PH-2 and F40PHM-2 locomotives being sent out for rebuild, there is an increased likelihood that the 611 and the 614 will be put back into service. Along with a small fleet of HEP-equipped EMD SD70MAC locomotives operating on the Alaska Railroad, the F40Cs are the last six-axle passenger locomotives in daily service in North America.
Metra plans to rebuild F40Cs 611 and 614 to test new prime movers and control packages. The rebuilt locomotives will be classified F40C-T3