Purpose. In this brief, cumulative county-level enrollment in Health Insurance Marketplaces (HIMs) through March 2016 is presented for state HIMs operated as Federally Facilitated Marketplaces (FFMs) and for those operated as Federally Supported State-Based Marketplaces (FS-SBMs). Enrollment rates in metropolitan and non-metropolitan areas of each state, defined as the percentage of “potential market” participants selecting plans, are presented. Monitoring annual enrollment rates provides a gauge of how well state outreach and enrollment efforts are proceeding and helps identify states with strong non-metropolitan enrollment as models for other states to emulate. Key Findings. (1) Cumulative enrollment in the HIMs in non-metropolitan counties has grown to about 1.4 million in 2016, representing 40 percent of the potential market in non-metropolitan counties. (2) Estimated enrollment rates varied considerably across the United States. In particular, estimated enrollment rates in non-metropolitan areas were substantially higher than in metropolitan areas in Hawaii, Illinois, Michigan, Montana, Maine, Nebraska, Wisconsin, and Wyoming. (3) The states that achieved the highest absolute non-metropolitan enrollment totals were Michigan, Georgia, Missouri, North Carolina, Texas, and Wisconsin. Of these, Michigan, North Carolina, and Wisconsin also had non-metropolitan enrollment rates above 50 percent. (4) About half of all states, evenly distributed by Medicaid expansion status but mostly concentrated in the Midwestern census region, had higher enrollment growth in non-metropolitan areas from 2015 to 2016, and in fact aggregated non-metropolitan growth was greater than metropolitan growth in both expansion categories.