Objective The objective of this study is to examine the impact of U.S. state online registration reforms on voter turnout. More states have been adopting online voter registration in recent years. Investigating the impact of the policy on voter turnout can inform policy making and contribute to our knowledge of political behavior.

Methods The methods of this study include difference‐in‐difference analysis and instrumental variable analysis. Using the Current Population Survey data between 2000 and 2014, I conduct a difference‐in‐difference analysis at the state level and then an instrumental variable analysis at the individual level.

Results The results of this study demonstrate that state online voter registration increases voter turnout. The difference‐in‐difference analysis shows that the states’ implementation of online voter registration increases the turnout of young voters by about 3 percentage points in presidential election years. The instrumental variable analysis shows that the usage of online registration by voters increases their turnout by about 18 to 20 percentage points.