Illinois weather
Illinois has four different seasons, ranging from cold winters to hot summers. By far the best time to visit is May-October, when temperatures are mild and fairly predictable. In winter the wind can make very cold temperatures even colder, dress very warmly if you're visiting then. Northern Illinois averages -4C in January to 24C in July. Southern Illinois averages 2C in January and 26C in July. The Chicago area next to Lake Michigan tends to get much more snow than the rest of the city.
Getting there
Chicago has two major airports, O'Hare and Midway. Midway is smaller and closer to the downtown. There are many other airports with regional service in the state, including in Springfield, Rockford, Peoria, Bloomington, and in St. Louis, across the river from Illinois.