CHICAGO (CBS) — Even before the polls opened for Election Day, voters in Chicago and suburban Cook County had broken records.

Chicago Board of Election Commissioners spokesman Jim Allen said, based on an unofficial count for early voting on Monday, voters in Chicago set a single-day record by casting 40,609 ballots.

In all, an unofficial total of 325,112 ballots were cast in early voting, topping the record of 260,000 set in 2008 by roughly 25 percent. With mail-in voting and grace-period registration ballots included, roughly 400,000 ballots were cast before Election Day in Chicago.

Suburban Cook County also set records for early voting, with more than 438,212 ballots cast between early voting, grace period voting, and mail-in voting, a 60 percent increase over the last presidential election. The previous record of 273,661 was set in 2012. The final day of early voting in suburban Cook County saw 42,107 ballots cast, besting the previous single-day record of 29,968 set only three days earlier.

The polls could be busy again on Election Day, based on the lines seen at many voting locations just after polls opened Tuesday morning.

“If early voting is indicative of how it’s going to be today, then I think we’re going to see a very healthy turnout, and it may exceed the prior presidential elections in 2008 and 2012,” said Chicago Board of Election Commissioners chairwoman Marisel Hernandez.

Cook County Clerk David Orr said, during the first hour of voting alone on Tuesday in suburban Cook County, about 1,000 ballots were cast per minute, and nearly 100,000 people had voted by 7 a.m.

This year, perhaps more than any other in recent memory, the fairness of the voting process has been called into question, with Republican presidential candidate Donald Trump repeatedly claiming the election is rigged against him.

But Hernandez said the city’s voting system is pretty much impossible to hack.

“We are extremely confident in our voting system,” Hernandez said. “If someone were to want to rig or to do something to these machines, they would have to go … and hack 10 to 15 thousand voting machines, because none are connected to each other.”

The Illinois Attorney General’s office said more than 190 teams of investigators would be working across the state on Election Day to make sure the voting process is protected and accessible to all.

Orr said several safeguards are in place both during early voting and on Election Day, to ensure the integrity of the election.

“Number one, we have Republican and Democratic [election] judges involved every process; through early voting, today at the elections, when we count mail ballots. They’re involved in every step of the way. Healthy competition is good,” he said. “We also do audits of everything we do. We have forensic testing to make sure there’s no malicious software. So there’s a lot of things we do to make sure things work. I don’t think people have to worry about that. There’s always probably some clowns that might try and cheat, but we’ve been pretty lucky over the past 20-some years in stopping that.”

All across Illinois, people are allowed to register and vote on Election Day, if necessary. Same-day registration and voting has never before been allowed on Election Day in a presidential election in Illinois.

That is expected to boost the number of voters at the polls on Tuesday.

The polls in Chicago close at 7 p.m. If individual polling places open late because of problems with machines or a lack of election judges, officials can ask a judge to order the polling place to stay open late to make sure everyone has a chance to vote.