Low-income adults who do not have children would be eligible for state-backed health care coverage under a measure approved in the Illinois House.
The Medicaid expansion is a signature plank of the federal Affordable Care Act.
Republicans protested the move because they say Illinois cannot afford it.
But House Majority Leader Barbara Flynn Currie says the state is already paying for people without insurance.
"The issue is not cost, the issue is who's paying. This pocket. Or the other pocket. You should know that the cost of uncompensated care in emergency rooms adds about $1,000 a year to your constituents' health insurance premiums. That is not going to go away." -Rep. Barbara Flynn Currie
The plan was approved on a partisan basis, and it's expected the same will happen as it goes to the Senate.
But even some Democrats voted against it, some are political targets and anything involving "Obamacare" is seen as controversial. There are also complaints that it does not go far enough. Dental care is not included.
It's expected the measure would add 500,000 people to Illinois' Medicaid rolls, though initially the cost is reimbursed by the federal government.
Illinois' plan also includes changes to policies that affect nursing homes and hospitals.
Illinois Public Radio's Amanda Vinicky contributed to this report.