The Centers for Medicare and Medicaid Services posted an update to the Health Insurance Exchanges Issuer County Map, showing projected issuer participation on the Health Insurance Exchanges in 2018 based on the known issuer public announcements through September 6, 2017. It is projected that 1,487 counties - over 45% of counties nationwide - could have only one issuer in 2018, representing more than 2.6 million Exchange participants with only one health insurance option and no other.
The Map can be obtained at https://www.cms.gov/CCIIO/Programs-and-Initiatives/Health-Insurance-Marketplaces/2018-Projected-Health-Insurance-Exchange-Coverage-Maps.html.