This article seeks to describe and explain variation in voter turnout in American big city municipal elections using data from 332 mayoral elections in 38 large U.S. cities over 25 years. In my cross‐sectional time‐series analysis of turnout in mayoral elections, I find that city‐level demographic factors are only weakly correlated with turnout. By contrast, institutional and campaign factors explain much of the variation. The effect of Progressive era reforms on depressing turnout is greatest in the most competitive elections. I conclude by discussing the implication of the overall downward trend in turnout and changes cities can make to increase participation.