Abstract Despite several decades of declining emissions, the health costs of particulate matter (PM_2.5) in the US remain substantial, with more than $1 trillion in annual damages. We analyze the inter-county impacts of PM_2.5 for 2008, 2011, and 2014 and find that even though emissions from point sources have fallen over this period, the share of PM_2.5 attributable to pollution transported across county and state boundaries is still considerable in many localities. Importantly, the benefits of reduced emissions are not uniformly distributed nationwide, with 26% of counties—concentrated in the South, Midwest, and Pacific Northwest—experiencing worsening health damages since 2008. Around 30% of all US counties receive 90% of their health damages from emissions in other counties, and these damage-importing counties also tend to have lower median incomes. Our results support continued state and federal cooperation to meet air quality standards and reduce the damages caused by PM_2.5 from transported air pollution.