What effect does moving to all-mail elections have on participation? On one hand, all registered voters automatically receive a ballot to return by mail at their convenience. On the other hand, the social aspect of the polling place, and the focal point of election day, is lost. Current estimates of the effect of all-mail elections on turnout are ambiguous. This article offers an improved design and new estimates of the effect of moving to all-mail elections. Exploiting cross-sectional and temporal variation in county-level implementation of all-mail elections in Washington State, we find that the reform increased aggregate participation by two to four percentage points. Using individual observations from the state voter file, we also find that the reform increased turnout more for lower-participating registrants than for frequent voters, suggesting that all-mail voting reduces turnout disparities between these groups.