The
Western Pacific Railroad Museum in Portola, CA has a sizeable collection (over 40, and I think only one steam loco), mostly EMD but including Fairbanks Morse, Alco, GE and Baldwin, from small switchers to a monster DDA40X 'Centennial'. Some of my photos here (from a visit in 2015, when I almost had the place to myself - they even let you climb on the equipment!) -
https://www.flickr.com/photos/135999716@N08/albums/72157662748370291
The Orange Empire Railway Museum in Perris, CA does have a few (and it's well worth visiting for the large collection of interurban and streetcars anyway).
+1 vote for the Illinois Railroad Museum (Union, IL) - it's got a huge collection of every sort of rolling stock, diesel, electric, steam, streetcar, interurban, railcars etc. This is a 'must see' museum, really.
(...and although it's not in a museum, Metra in Chicago still has an EMD SW1 switcher in use as a workshop/yard switcher, dating from the early 1940s. This is one of the oldest operational diesels in the US).