Chicago has two major airports: O'Hare and Midway. O'Hare International Airport is located inland, and is one of the world's busiest. Midway serves domestic flights and is located 13km southwest of the Loop.
Taxis are available around the clock. They charge 1.5 times the regular fare to get to the airport. It can be a little expensive, but is the most convenient way to get where you need to go.
The Blue Line of the L runs to O'Hare, but can take up to an hour to and from the Loop. An express line is in the planning stages (as it's been for decades). Midway is about twenty to thirty minutes from the Loop along the Orange Line. One trip will cost $2.25 without a pass.
The Continental Airport Express shuttle vans serve most of Chicago's finer hotels. Ticket counters are located at both airports near the baggage claim.