If you are anywhere near water in spring at twilight or dawn, it's likely you will hear a very loud chirping sound that almost sounds like bells. This is the call of the spring peeper, a tiny frog that breeds during the beginning of the spring.
Spring peepers are native to the eastern U.S., and they are common in Illinois. The loud noise comes from the males calling out to females, hoping to mate. They are some of the first frogs to begin calling in the spring, so you know it's definitely getting warmer when spring peepers start chirping.
Spring peepers have some interesting traits that allow them to come out this early in the spring. They can endure temperatures below freezing for short periods of time, enough to get through the wild fluctuations of Illinois' early spring weather. They are able to tolerate their body fluids freezing, and they can come out of that catatonic state perfectly well after they've defrosted. This usually tends to happen in the more northern parts of the spring peepers' range, but with the weather in Illinois being so strange lately, it is a useful trait to have here as well.
If you're looking for spring peepers (or any other frog, for that matter), they're usually hidden on the edges of marshes and ponds, nestled between the reeds. Walking on the edge of a pond usually causes enough disturbance to make them jump out into the water, since they can sense very small vibrations. Sometimes a whole cascade of frogs can jump from the side of a pond, even if you are keeping your steps quiet. Try walking along the water's edge in the morning this spring. You just might see a spring peeper.