While this site is very close to home for me, I haven't been there diving in a number of years, so my firsthand knowledge is limited. My recollection was that vis was limited, but again, it has been a number of years.
"Close to home, the Chillicothe Recreational Area actually consists of three gravel pits, one of which is open for scuba divers. Depths range from 10 feet to 26 feet. Fish life is varied, and includes sun fish, bass, crappie, cat fish & carp. If you swim slowly, you may spot turtles in the shallows or along the bank at the east end of the lake. It is one of the few lakes in Illinois where divers can find freshwater jellyfish in the early spring and late fall. A number of man made objects, including a school bus, several boats, & dive platforms may be found. The best diving is generally along the east or north shores of the lake. The west end is very shallow and tends to get weed choked. Entry fee is $15. C card required. Surface amenities are minimal. There are no equipment rentals on site, so bring what you need.
Nearest air fill station: Do Dive In
Chillicothe Recreational Area
20205 N Route 29
Chillicothe, Illinois"
From Do Dive In website.
See also
Chillicothe Recreation Area | Chillicothe IL 61523 United States | Dive Site | DiveBuddy.com
I don't believe you can get air fills on-site, but the Peoria area is blessed with 3 local dive shops. If you are coming in from St. Louis, your time is likely best served by stopping in Morton at Aqua Diving School (a short jog off I-74) on the drive in if you need a fill. Both Deep Blue Adventure and Do Dive In are also great shops (and where I get my fills), they're just a bit more out of your way.
If you feel like diving there sometime, send me a PM--I'm always looking for someone to dive with!