Partisan media exerts a powerful influence on American politics. Yet what precedes such media effects---exposure---has attracted little-to-no attention. A survey of relevant literature gives us an inconsistent picture of the extent to which Americans are exposed to partisan media, with the realities of a multi-platform information environment complicating the task of obtaining an overall snapshot of exposure at any given time. We focus on the most popular partisan news source, Fox News, and ambitiously assemble all available data on direct exposure (i.e., Nielsen TV ratings, web traffic, Facebook, Twitter, YouTube, Instagram, and self-reports) for a one-month period. We find that across all measures, American exposure to Fox News is relatively limited—except for self-reported consumption in surveys. These inflated measures, when aggregated and disseminated, create a false impression that many other Americans are regularly consuming Fox News. Our survey experiment shows that misperceptions grounded in this third-person effect of exposure are mostly resistant to corrections and contribute to partisan stereotypes and polarization.