PINAL COUNTY, Ariz. - Pinal County could become the first county in the United States to lose Affordable Care Act coverage after Aetna's announcement that it's pulling out of Arizona.

Aetna's withdrawal follows the exit of UnitedHealthcare and Humana from Arizona. Blue Cross Blue Shield of Arizona and Health Net announced in June they would end coverage in Maricopa and Pinal counties.

The mass exit by the health insurers, all citing financial losses, will force tens of thousands of Arizonans to look for new coverage next year from a dwindling pool of providers. Several rural counties have just one health insurance option on the Obamacare marketplace next year.

Statewide, 200,000 people are insured under Obamacare, according to the U.S. Department of Health and Human Services. About 126,000 Maricopa County residents are insured; 9,700 people in Pinal County are covered.

"Things could change, but that's not probable," said Alan Gjersvig, who directs ACA enrollment services for the Arizona Alliance for Community Health Centers.

Gjersvig said one of the remaining insurers offering ACA plans in Arizona could work with the Arizona Department of Insurance to offer plans in Pinal County. The deadline for offering new plans in Arizona was this month.

A spokeswoman for the Insurance Department could not be reached for comment.