About 1.3 million seniors could benefit from the plan, according to the Illinois governor's office.
"I save $35 a month on it, that's what's great. I can go on the bus anytime I want," said Jay Gunansky, CTA Rider.
"I never thought I'd live to see this: I could ride the CTA for free? It's truly a blessing," said Ollie Williams, CTA Rider.
Governor Rod Blagojevich was at a CTA Blue Line station on the city's Northwest Side to mark the start of the free rides.
"You're gonna get out more, not just to the doctor, not just to see the grandkids, not just to go to the grocery store. You're gonna get out more," said Gov. Blagojevich.
The free rides for Illinois seniors are available on all mass transit in the Chicago area, including CTA buses and trains, PACE suburban buses and Metra trains.
Seniors must sign up for the plan. Already, 30,000 of them have, according to the state. Those with reduced fare cards were automatically entered in the program.
Critics - including some seniors- question the $15 million estimated cost to provide free rides.
"Things were bad, with doomsday. I thought it was silly to do this - they need the money. But I had no choice, so I'm glad now," said Judy Hedberg, CTA rider.
"We can afford to do this, because you worked hard all your lives. We can't afford not to do this. It's the right thing to do for our senior citizens," said Gov. Blagojevich.
To Register for Senior Plan
To find a registration site near you, click here. You can also call the RTA Travel Information Center at 836-7000 from any area code.
For more information on the program, visit RTAChicago.com