CHICAGO (CBS) — Chicago had its best midterm election turnout since 1986 on Tuesday, and election officials credited millennials for the big boost in voters.

Overall, 56 percent of registered voters in Chicago cast a ballot in the election, either in person on Election Day, during early voting, or by mail.

Turnout was slightly lower in the Cook County suburbs, where 52 percent of registered voters cast ballots, but figures in the city and suburbs could increase slightly, as there could still be uncounted ballots in the mail.

Cook County Clerk David Orr was excited to see so many people at the polls.

“The key is lots more people voted than four years ago. So all the rumors you’ve been hearing are true. So it was not just early voting. It was overall turnout,” he said. “It’s really nice to see this many thousands of people voting.”

In Chicago, the largest voting group was millennials. Approximately 28 percent of voters were between 18 and 34 years old.