It seems we've found a way to measure everything— and we do. But finding the particular statistics you're looking for can be just as daunting as working with the data itself!
Chicago Board of Trade, 1970. National Agricultural Library.
These pages should help. By far, the largest most comprehensive and most reliable producer of statistics come from government agencies. For agriculture, the USDA is the best place to start - you'll find a breakdown of their major publications in the following tabs. We also link you to relevant non-government sources.
Data can be available either online or in print (or both). Most recent data is likely online, though some publications still offer print. We've separated the tabs by Illinois, National, International, and Historical, but browse through all three— data sources can overlap.
The lists here are extensive, but by no means comprehensive. Try a catalog search for the specific data you need. If you're in need of further assistance, come visit us at the Funk ACES Library Reference Desk - we'd be happy to help.