In the summer of 1978 had occaision to drive west from my home in the Waukegan, IL area, to Byron, IL. Byron is on the Rock River, south of Rockford. The Milwaukee Road's "Southwestern" line (going to Ks City) ran through town and the Milwaukee was in the process of tearing down it's depot there. Since the door was swung wide open, walked in and found debris strewn everywhere. But, noticed this forms cabinet torn off the wall, and thought, "Hmmm, looks like a pretty useful item." It almost miraculously fit in my tiny Honda hatchback Civic, with only molecules to spare !
Hauled it home, stripped the awful boxcar red it had been painted, sanded it, etc. for a couple of months and stained it cherry. The result was a perfect cabinet with an abundance of 2 inch slots, in 3 banks, perfect for my collection of railroad historical society publications.
My guess is it was constructed with the depot by Milwaukee Road carpenters in about the 1905 era.