And Harken's parent, UnitedHealth, earlier this year said it would itself exit most Obamacare exchanges, including the federal marketplace that services Illinois, in 2017.
Harken, in statement to CNBC, said, "Harken Health remains committed to our innovative model of insurance paired with access to relationship-based care and we look forward to continuing to offer plans to individuals and employers who purchase coverage outside of the exchange."
The Chicago Tribune noted that because of Harken's exit from the exchange, residents of Cook County, which includes Chicago, will have just three insurers to choose from if they want to buy coverage on HealthCare.gov, the federal Obamacare exchange that serves Illinois and 37 other states.
HealthCare.gov and state-run Obamacare exchanges are the only places that low- and moderate-income customers receive subsidies, in the form of federal tax credits, to lower the cost of their monthly premiums.
The subsidies, whose amounts are linked to income levels and the premium charges, can significantly reduce the cost of coverage.
People who buy Harken Health plans, or any other individual plans, outside of the exchanges must pay the full premium.