Construction is already underway on the final runway to be built in the O'Hare Modernization Program.
The city said the project means more planes can take off here at the world's busiest airport. The FAA said the expansion has already allowed dozens more planes to take off each hour.
The city has been in the process of shifting and extending the runways for more than a decade, and expects to complete the remaining runway work in the next two years.
Leaders called this modernization and the ongoing O'Hare 21 project vital to keeping Chicago at the center of the flying world.
The city said these upgrades are creating over 60,000 new jobs, some of which will be around a decade.
In March, the Chicago City Council approved the $8.5 billion upgrade at the airport.
Other upgrades under the O'Hare Modernization Project include a new global terminal, as well as other improvements.
The council's Finance Committee also approved a measure to borrow $4 billion to start the eight-year project in March.
The project would expand O'Hare's capacity and improve travelers' experience. It would be the largest and most expensive revamp in the airport's history.
Gates would increase from 180 to 220, reducing flight delays and expanding travel options for customers.
New self-service technologies will allow passengers to quickly check in for their flight and drop off their bags. Security screening updates aim to enhance security and further reduce passengers' wait times.
Terminal 2 would be replaced with a new global terminal, and Terminals 1, 3 and 5 would be substantially expanded.
All the improvements are expected to be completed by 2026.
"That sounds good, it just sounds a little concerning about what the situation at the airport is going to be like while that's all happening," said Emily Bleibel, a Chicago traveler.
"As long as I'm not standing in longer lines, that's great," said Justin Klehm, another traveler. "Love flying out of O'Hare."
The project is slated to not include taxpayer money, instead be paid for by the airlines. United and American would each get expanded capacity as part of the upgrades.
The city believes the new O'Hare will pump $50 million into the Cook County economy annually.
Former mayor, Rahm Emanuel, called the upgrades Chicago's "boarding pass to a bolder and brighter future."
After the vote in March, Emanuel and airline representatives from United, American, Delta and Spirit airlines inked new use and lease agreement to expend O'Hare.