The next step may be more difficult: Quinn hopes to get the Legislature's approval for a state-based exchange to offer coverage in 2015. The state would have more authority over how the exchange would be run in a state-based model, but Quinn hasn't yet been able to get that off the ground.
Quinn, a Democrat, said Wednesday that a state-based exchange remains his goal, and that he has support from two key Democrats, House Speaker Michael Madigan and Senate President John Cullerton.
"The speaker of the House and the president of the Senate have made it very clear to me that they support the legislation," Quinn said. "I think we have good majorities and people want to do the right thing."
Sebelius' letter acknowledges that "Illinois is working under intense timelines." At the press conference, she praised Quinn as "a great governor and a great leader in health care."
With the Illinois approval, 20 states and the District of Columbia have been conditionally approved to partially or fully run a health insurance marketplace, also known as an insurance exchange.
The exchanges are a key part of the Affordable Care Act, the health care law that is reshaping how Americans buy insurance.
Beginning Oct. 1, people without health insurance will be able to sign up for government-subsidized private coverage through the new exchanges. Coverage will start Jan. 1. Low-income people will be steered to the expanded Medicaid program.
Most Americans will be required to have health insurance, either through an employer, a government program, or by buying their own commercial plan. The subsidies available through the exchange would mean a $10,742 tax credit toward an annual $12,130 insurance premium for a family of four making $35,000 a year.
Nearly 1.8 million Illinois residents are uninsured. An estimated 486,000 Illinois residents will get coverage from commercial insurers through the exchange in 2014. That figure is expected to reach 1 million customers by 2016.