The effectiveness of health insurance advertising has gained renewed attention following the Trump administration's decision to reduce the marketing budget for the federal Marketplace. Yet there is limited evidence on the relationship between advertising and enrollment behavior. This study combined survey data from the 2014 National Health Interview Survey on adults ages 18-64 with data on volumes of televised advertisements aired in respondents' counties of residence during the 2013-14 open enrollment period. We found that people living in counties with higher numbers of ads sponsored by the federal government were significantly more likely to shop for and enroll in a Marketplace plan. In contrast, people living in counties with higher numbers of ads from political sponsors opposing the Affordable Care Act (ACA) were less likely to shop or enroll. These findings add to the evidence base around advertising in the ACA context.