Not a hump yard, but Norfolk Southern’s Decatur (IL) Yard is rather large. I believe this is (or was) the largest flat-switching facility in the NS system.
Alton & Southern is owned 100% by UP and is in E. St. Louis, Ill. It has a North and South hump tower. It has 66 classification tracks in the bowl and humps aprox. 2,400 cars in 24 hrs. They have a contract to do the 1,000 mile inspection for the BNSF oil trains.
TRRA’s hump is in Madison, Ill. It has 40 classification tracks but does less than half of the A & S daily volume.
Check out “North American RAILYARDS” by Michael Rhodes. It covers both US and Canada.
I recommend “North American Railyards” by Michael Rhodes (ISBN 978-0-7603-1578-1). The most recent edition is 2003, so it’s a little dated in that some of the yards may no longer be operating. It’s organized by railroad and covers a lot of yards. Not the definitive work of ALL railyards, but it’s a good read.