In a Friday, May 6, 2016 photo, LSU medical student Felicia Venable, left, briefs fellow students and medical residents on a patient they are visiting during daily rounds with a group of medical residents and medical students at Our Lady of the Lake Regional Medical Center in Baton Rouge, La. Gerald Herbert/AP Images Pinal County, Arizona, right next to Phoenix, was founded in 1875 and is home to roughly 400,000 people.

It's also the county that Obamacare forgot.

After Aetna's announcement that it will roll back 70% of its offerings in public exchanges, Pinal County appears to be the only county in the US with a public exchange but zero insurers offering Affordable Care Act plans in 2017.

This leaves people that need insurance through the ACA in Pinal County with limited options. Currently, Blue Cross Blue Shield of Arizona is participating in the county, but it has plans to pull out in 2017.

According to Cynthia Cox of the Kaiser Family Foundation, a nonpartisan healthcare-focused think tank, convincing BCBS to stick around seems to be the easiest option.

"Plan A is to try and work with the Blue Cross Blue Shield in that state or another provider in the state to get them to move in," Cox said. "The question is if there is any plan B."

The plan B could simply be that there is no exchange offering and people have to buy insurance on their own, but that presents issues as well.

"If that's the case, it's mostly going to be unaffordable for those who are already receiving subsidies," Cox told Business Insider. "They're no longer going to be eligible for the subsidies, and it is likely that private coverage is not going to be affordable without the subsidies."

Cox said that these people would not be subject to any penalties under the individual mandate, but if they were injured or got sick during the year, they "could be faced with significant medical bills."

To be fair, even before Obamacare, many areas of the country had limited options when it came to health insurance, but that probably isn't much relief for people in Pinal County and other places around the US.

Even if BCBS stays in Pinal County, the situation will be far from ideal.

The number of insurers available and competing in a market is linked closely to the cost of premiums, and the withdrawals are leaving more and more areas with only one or two insurers. With that sort of monopoly or duopoly, premiums can increase even more than they already are.

Cox told Business Insider that the situation in Pinal County will likely raise calls for a public option, or a government-run health insurance option similar to Medicare or Medicaid. This would provide an insurer of last resort for a county like Pinal and would drive competition where there are limited private options.

As it stands now, however, there is no such option for Pinal County and it appears that unless someone steps in, there will be an Obamacare marketplace, but no one selling anything in it.