Normally, when entering the US (anyone making a connection still needs to enter the US), you need to collect the baggage, go through customs and re-check the baggage on the connections belt.
However, you will enter the US at Toronto (rather than Chicago), and thus already be customs-cleared on arrival in Chicago, whereby you'll end up directly in the departures lounge. As such, since it's a single ticket, the baggage will be checked through.
This also means that if your flight to Chicago should be very late and you end up missing the connection, your onward trip is the responsibility of the airline. However, unless it is late, you will make the connection for sure.