Please be aware that Chicago has multiple airports and that these results are only for O'Hare International airport.
The best day to arrive at Chicago is Saturday and it would be best to avoid Tuesday, as prices are on average 221.93% higher than on Saturday. (Average prices, based on 204 datapoints.)
At Chicago the most flights depart around 11:00. (Hourly flights, based on 359 datapoints.)
From Chicago it is on average the cheapest to fly to Toronto and to Frankfurt. (Average prices, based on 103 datapoints.)
From Chicago most of the flights depart to Toronto, second best connected from Chicago is New York. (Daily flights, based on 88 datapoints.)