Public opinion about the Affordable Care Act (ACA) has been polarized since the law's passage. Past research suggests these conditions would make any media influence on the public limited at best. However, during the early phase of implementation, locally broadcast ACA-related media messages—in the form of paid health insurance and political advertisements and news media stories—abounded as advocates, insurance marketers, and politicians sought to shape the public's perceptions of the law. To what extent did message exposure affect ACA perceptions during the first open enrollment period? We merge data on volumes of messaging at the media market level with nationally representative survey data to examine the relationship between estimated exposure to media messaging and the public's perceptions of how informed they were about and favorable toward the ACA in October 2013. We find that higher volumes of insurance advertising and local news coverage are associated with participants’ perceptions of being informed about the law. Volumes of insurance advertising and of local news coverage are also associated with participants’ favorability toward the law, but the relationship varies with partisanship, supporting the growing body of research describing partisan perceptual bias.