In general, when looking for the cheapest flight to Chicago, try to choose a flight departing in March for the best deal.
In general, most flyers find the cheapest time to book a flight to Chicago is about 12 days prior.
Most of our users find that booking their departure to Chicago on a Tuesday is the cheapest. Conversely, departing on a Saturday seems to be the most expensive.
Generally, when visiting Chicago, morning flights represent the best value. afternoon flights are likely to have higher prices.