I've been to Haigh a number of times. Check out the map they provide:
Quarry Map - Haigh Quarry - The Place for Scuba Diving in Northern Illinois
(Notice, North is on the left-hand side.) The only entrance to the water in the quarry is on the West side. On that side, there are two "main" entrances to the water. One is from the "beach" and the other is from a floating dock. The "beach" is sand mixed with crushed stone, not so easy on bare feet or equipment. The pro's to this spot, easy access to the water and exit. It is close to the buoyancy course. Close to the shallow end. If you get their early, you can park really close, if the operators of the quarry allow you. It is also close to the food stands. The con's: This is a very small area with lots of congestion. If you're going to setup there, be sure to put down a tarp to protect your equipment and feet and weight the tarp down (it can get windy). It is in direct sunlight all day long and it can get hot.
The floating dock is directly to the south of the "beach" and it is surrounded by grass. Pros: It is a tree shaded area, for the most part, and is much cooler then the beach. Grass is nice to walk around upon. You can park somewhat close, if you get there early. You can setup a canopy. The dock has benches to gear-up. You can practice your giant stride entrance. Much deeper water (30+ feet) to enter. Easy access to the sunken boat, The Flamingo, the LARC and other things. Cons: Much Colder water, the spring source is very close. It can be kind of dark at times. Buoyancy course is a long swim away.
Overall, check out their web site for more details. They provide grills there, so you can grill if you bring food and charcoal. They have wooden park benches everywhere, which is helpful to gear-up, but try to leave them for other people while you are diving.
My advice, bring a cooler and plan on getting there early. Before you arrive, stop at the giant K-Mart which is on the way there. It has a HUGE supermarket in there. Stock up on liquids, food and ice. Cool?