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Taking the train to Joliet will be significantly cheaper than renting a car, but will take up to 3 hours from the airport, depending on where and when you arrive.
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The Texas Eagle provides direct service from various cities between San Antonio and Chicago. Returning from Joliet to Chicago, avoid the Texas Eagle as long distance train have miserable on-time performance (56.7% for train #22 in June 2010).
Arriving at O'Hare and Connecting to Amtrak
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Allow 40 - 60 minutes to make this transfer, depending on your comfort with transit.
Metra
Metra
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serves Joliet via Rock Island District trains. Very limited service is also provided on the Heritage Corridor, but only during rush hours. Rock Island District trains leave from LaSalle Street Station and arrive at Joliet Station. Service is provided roughly hourly during the week and every two hours on the weekends. Travel time is 60 - 90 minutes.
Arriving at O'Hare and Connecting to Metra
After collecting your bags, follow the signs to "CTA Trains" or "Trains to City", which will take you to the CTA Blue Line.
Exit at LaSalle and walk west about half a block.
Allow 60 - 90 minutes to make this transfer, depending on your comfort with transit.
Arriving at Midway and Connecting to Metra
After collecting your bags, follow the signs to "CTA Trains" or "Trains to City", which will take you to the CTA Orange Line.
Exit at LaSalle and walk west about half a block.
Allow 40 - 60 minutes to make this transfer, depending on your comfort with transit.