I Agrew up about 20 miles from there. I remember that there was a huge icing platform there. From the highway you could see the crews loading ice blocks into the reefers. This was a very labor intensive operation in the 50’s.
Perhaps the St Clair County Historical Society would have something on the web.
Also, there is a railroad history group which focuses on the RR’s which served the St. Louis area. I don’t know the name of the group, but the owner of Red Board Hobbies in Belleville, IL could probably tell you how to reach them. I have seen some very detailed RR maps put together by the group.
If you are in Dupo visiting the family head for the hobby shop that faces the yard, Stewart’s Hobbies I believe it is called. Not only does he have an elevated observation deck over looking the hump-yard, but he has some historical photos of the yard on display on the walls of the store.
Mainline Modeler magazine ran an article about the Dupo yard around 1995 or 96, which included several photos taken during that time period, but I no longer have back issues.
The maps I have (1941) just show two rail lines along the west edge of the town and say things like “MP roundhouse and yards beyond” and “full of tracks”. If the wording of where it says roundhouse is really significant it is west of Dryroff Avenue.
There are a couple details that perhaps you can combine with other references to help:
There is one siding to the east that splits from the main (looks like a double track main) at “Godin” street. It parallels N. Main (also called 1st street?) for about 1.5 city block and ends (butts into) at some gasoline storage tanks. Lindman Blvd is just to the south of this. I don’t see any industries along this siding so it is possibly a team track.
Just south of Lindman Blvd is the passenger station. This is where Main angles off to the east. If it didn’t the station would almost be in the center of the road.
The water tower is just a bit south from the station (about where south 2nd meets S. Main).
There is a turnout on the west main branching to the north at about McClure street. Cannot tell where it goes to.
The EStI&C, Mopac, and IC all cross and meet at about where State Highway #3, Falling Springs Avenue, and 4th streets meet. The IC runs E-W, the MP is almost N-S, and the EStI&C is going NW-SE
The Cotton Belt had trackage rights through Dupo on this part of the MP from Valley Junction, IL to North Junction, IL for a total of 119 miles. The Cotton Belt’s primary yard in the area was at Valley Junction about four miles north of Dupo.