John - Mississauga is a city of 600,000 or so people that abutts the west end of Toronto.
Often this area is refered to in a larger sense as part of the GTA - Greater Toronto Area, which counts about 2.5-3million in population.
I am about 20 minutes from downtown Toronto, as long as the trip is not made in rush hour.
I have yet to google Galesburg, but have travelled through Illinois on holdays though the years. Not spectacularly different in the geography, though you might have a bit milder winters.
The GTA is not as sprawling as greater Chicagoland.