The midterm elections are just six weeks away on Nov. 6.
"Early voting and midterm elections never seem to be on people's radar and this year, it's not a choice. It's not an option. We have to do it," said cast member Amanda Clement.
The cast was trained to register people on the spot at the CIBC Theatre in the Loop.
"I follow 'Hamilton' on Twitter so I was like, 'That's perfect because I'm not registered in Chicago.' So I just stopped here on my lunch break," said Hannah Grace, who's from Arkansas and needed to register to vote.
Miguel Cervantes, who plays the title role of Alexander Hamilton, also registered to vote in Illinois.
"It's important for us to relay the message that we're giving every night to here in the real world to say this is how you can rise up and make your voices heard," Cervantes said.
To vote in Illinois, a person must be 17 years old on or before the date of the primary election, and turn 18 on or before the date of the general election.
Registration can be done online, via mail or in-person.
In Cook County, voters can register online until Oct. 21. The first day of early voting is Oct. 22.
Voter registration drives sought to draw in young people, who comprise a large percentage of the electorate, but usually don't turn out to vote.
Kayle Crane, 20, did her part to change that on Tuesday.
"The younger generation should come out and register to vote because i feel like we do have a voice," Crane said.
Cook County Clerk David Orr popped in on the "Hamilton" voter registration drive after attending a voter event organized by the Illinois Coalition of Immigrant and Refugee Rights.
"We're in a struggle for democracy. An absolute struggle. And if you don't pay attention, you might lost the freedoms you so cherish," Orr said.
For more information, visit vote.gov.