in Madison WI sponsored by the NMRA South Central Wisconsin Division.
More info here. https://www.nmra-scwd.org/scwd-events.html
It's one of the better shows in the upper midwest. Unlike Milwaukee's Trainfest, the Mad City show features plenty of dealers in used and "swap meet" type stuff, along with the usual dealers in model and toy trains and rail collectibles, display layouts, railroad historical societies, and so on.
Dave Nelson