The mayor spoke with reporters at O'Hare about an hour ago.
The new project will feature a 4,000-space rental car facility, along with new public parking areas. The project is expected to be completed in 2016.
The project is projected to create 3,000 construction jobs and 100 permanent jobs.
"This will allow people who either rent a car, park, or public transportation, get to and from the airport so they can get to and from their destination with a level of convenience," said Mayor Rahm Emanuel.
The mayor says a nearly $300 million government loan will help break ground on the new development that's designed to cut down on traffic congestion around O'Hare.