Interactive Maps: Estimates of Enrollment in ACA Marketplaces and Medicaid Expansion

As the 115th U.S. Congress deliberates the future of the Affordable Care Act, an interactive map from the Kaiser Family Foundation provides estimates of the number of people in each congressional district who enrolled in a 2017 ACA marketplace health plan and the political party of each district’s representative as of October 2017.

The analysis also includes maps charting the total number of people enrolled under the ACA Medicaid expansion in 2016 in states that implemented the ACA Medicaid expansion, along with the political parties of their governors and U.S. senators. As of October 2017, among states that adopted the Medicaid expansion, 17 have Republican governors, 13 have Democratic governors, and one has an Independent governor. In Washington, D.C., which also expanded Medicaid, the mayor is a Democrat.

The map below shows estimates of ACA Marketplace enrollment as of March 2017 by congressional district, with red and blue districts representing those with a Republican or Democratic congressional representative. In New York and Minnesota, Basic Health Plan enrollment is included in the estimate of Marketplace enrollees.  Districts with darker shading have a greater number of Marketplace enrollees. The map includes estimates of enrollees with advance premium tax credits and cost sharing reduction in 2017 for congressional districts in states using

Explore 2017 ACA Marketplace enrollment By Congressional District with this @KaiserFamFound interactive map

Of the 10.3 million Marketplace enrollees and 730,000 Basic Health Plan enrollees nationally, 5.9 million live in Republican districts and 5.2 million live in Democratic districts. Marketplace enrollees per Republican district range from 9,000 enrollees in West Virginia’s District 3 to 88,400 enrollees in Florida’s District 27, with a median of 22,000 enrollees per district. Marketplace enrollees per Democratic district range from 6,600 enrollees in Hawaii’s District 1 to 87,200 enrollees in Florida’s District 24, with a median of 24,200 enrollees per district. The ten congressional districts with the highest number of Marketplace enrollees are all in Florida. There are 22 congressional districts (7 Republican districts and 11 Democratic districts) with over 50,000 enrollees, located in the following states: Florida, New York, Georgia, and Utah.

Number of People Enrolled in ACA Marketplaces in 2017, by Congressional District

As of October 2017, 32 states including the District of Columbia implemented the ACA Medicaid expansion to adults. This expansion extended Medicaid eligibility to many adults who were previously excluded from Medicaid. In 2016, about 15 million Medicaid enrollees were adults in the expansion group.  This group includes those who were made newly eligible by the ACA Medicaid expansion as well as a smaller group of enrollees who were eligible for Medicaid through pre-ACA eligibility pathways (see methods for more details). The expansion group accounts for 20% of all Medicaid enrollees. Since 2016, this number has likely grown as enrollment has continued to increase.

Number of People Enrolled in Medicaid Expansion in 2016, by State Governor’s Party

The map below shows the number of people enrolled in each state’s Marketplace (as of March 2017) and through the Medicaid expansion (as of December 2016). The map also shows the number of enrollees with advanced premium tax credits in each state, the estimated total annual premium tax credits received by enrollees in state marketplaces, and the number of enrollees with cost sharing reductions in each state (as of March 2017). States are color-coded by the U.S. Senators’ party affiliation with red states representing those with two Republican senators, blue states being those with two Democratic senators, and purple states having both Republican and Democratic senators. As of March 2017, 3.5 million Marketplace enrollees live in red states, 4.6 million live in blue states, and 3.0 million live in purple states. For blue states, this number includes Basic Health Plan enrollees in New York and Minnesota. In 2016, about 1.7 million Medicaid expansion enrollees lived in red states, 10.5 million lived in blue states, and 2.8 million lived in purple states. (Washington, DC does not have a senator, so its 122,200 enrollees are not included in these totals).

Number of People Enrolled in ACA Marketplaces (2017) and Medicaid Expansion (2016), by Senators’ Party


Marketplace enrollment by congressional district as of March 2017 is estimated using county-level plan selection data (from ASPE for states, and from state reports for State-Based Marketplaces). Because not all people who selected a Marketplace plan paid their premium and effectuated their coverage, adjustments were made to match each state’s effectuated enrollment totals. For Minnesota and New York, Basic Health Plan (BHP) enrollment is also included. Estimates of enrollees with advance premium tax credits and cost sharing reductions are not available for state-based marketplaces because county-level advance premium tax credit and cost sharing reduction data is not available in these states. A county/congressional district crosswalk was created using data from Missouri Census Data Center and state reports for the three states that have been redistricted (Virginia, North Carolina, and Florida). For counties that cross congressional district boundaries, enrollment was proportionally assigned based on the percent of the county population living in each congressional district. Enrollment is rounded to the nearest 100.

Medicaid enrollment is from both the Medicaid Budget and Expenditure System (MBES) and the California Department of Health Care Services report is reported for each month. In an effort to take into account that some beneficiaries are enrolled for only part of the year, maximum monthly enrollment for each state is used to estimate total annual enrollment. Enrollment is rounded to the nearest 100. States totals may not sum to national total due to rounding.

Expansion Group Enrollment: Total number of adults who have enrolled in Medicaid as a result of the ACA expansion of the program.  This includes those made newly eligible for Medicaid by the ACA Medicaid expansion and some enrollees in the expansion group who were eligible for Medicaid through pre-ACA eligibility pathways. The not newly eligible enrollees group includes some childless adults in early expansion states as well as those who may be subject to technical adjustments. Some states already provided coverage at the traditional match rate to parents and adults without dependent children up to at least 100% FPL statewide as of March 23, 2010, when the ACA was enacted.  The law provides additional federal funding to these states through the “expansion state match rate” for adults without dependent children under age 65; this “expansion state match rate” is higher than the traditional match rate.  In addition, a few states were able to make adjustments to account for individuals who would not have been eligible because of asset test requirements in place on December 1, 2009, enrollment caps in effect for waiver populations receiving full benefits as of December 1, 2009, and other special circumstances. These adjustments may result in some adults being enrolled in the expansion category who do not qualify for the 100% federal match for newly eligible adults.

More information on the methods for estimating Medicaid expansion enrollment can be found here.

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