Illinois has been a slug-hunting only state for the long, long time.
Illinois had no "big game" seasons until 1957. Deer we considered nearly extinct when my grandfather was a kid in the 1920-30's. He and my father used to tell me it was big news when one was sighted. Hard to believe today with deer everywhere. Anyways when the original modern seasons were established 1 there weren't very many deer so harvests needed to be modest, 2 popular theory at the time that a pumpkin ball slug traveled less distance and therefore was safer than rifle bullets, and 3 shotguns were already the commonly owned firearm most farmers and sportsmen used for small game. Sadly there was also political pressure not to make rifles "socially acceptable" (the whole weapons of war thing).
Regardless, the rules stuck and nobody much cared when I started hunting here in the 1980's. There were plenty of rifle shooters at the clubs, but for the most part a 12 gauge pump with two barrels and maybe a 22LR rifle were the standard hunting rigs for everyone I encountered for everything from squirrels and rabbits, pheasants and ducks, up to deer.
The explosive growth in the deer herd and greater interest in deer hunting over the past twenty years has driven a lot of innovations with new slug designs, rifled barrels, and scoped receivers making them effective 125 yard big bores. Frankly without the rifle restrictions there would be no sabot shotgun slugs, no rifled shotgun barrels, and most likely no inline muzzeloaders. These were all technologies developed specifically to give centerfire-like options to people stuck in slug zones.
For about 35 years the choices were simply archery (long season, low success) or shotgun (very short 3 day season, good success). However in the past twenty years as the deer herd surpassed 750,000 animals Illinois greatly expanded the seasons to add more tags, more days afield, and additional weapons. Muzzeloaders, inlines, larger caliber handguns and crossbows were legalized and are very popular.
Other states around us that were traditionally also restricted to shotguns have similarly expanded weapon choices. A few have recently included rifles chambered in the same 35 caliber and larger straightwall cartridges already approved for handgun seasons. Those rifles have been flying off the shelves where they have been allowed as fall hunting season approaches. Heck I would trade a slug gun or inline for a lever action 45-70 or 44 magnum any day!
If the other shotgun states fall in line with these changes, I can easily foresee shotgun slugs and inline muzzleloaders getting swept away. Anywhere rifles of any flavor are allowed other weapon types become a quaint annomoly. Frankly all of my hunting friends are looking forward to it.
For a quick history on Illinois deer hunting, check this:
http://web.extension.illinois.edu/deer/historyofmanagment.cfm
