The coroner's office said Petter Culver, 75, of McHenry was working as an election judge at McCullom Lake Village Hall when he suffered a cardiac event.
The coroner's office was alerted about 9:15 p.m.
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McCullom Lake police also investigated the incident, but officials determined Culver died from natural causes.
"I want to thank (County Clerk) Mr. (Joe ) Tirio and his team for the professionalism they showed during this unusual and unfortunate event," the coroner's office said.
Tiro released a statement that said:
"Last night, as the polls closed and the final ballots were counted, we lost one of our own. Petter Culver passed away doing something he believed in deeply - serving his community as an election judge.
"Petter gave years of faithful service to the Democratic Party and the democratic process in McHenry County. He served because he understood something that too many take for granted: freedom is not self-sustaining. It requires tending. It requires people willing to do the hard and unglamorous work of making democracy real - not just in theory, but in practice, one voter at a time.
"That work is hard. Let no one tell you otherwise. Our election judges report before dawn and work well past nightfall, fifteen hours or more staying at their post with little opportunity for a break. Most of our judges are past the age of 65, and yet they lift equipment, set up polling places, navigate complicated procedures, and do it all with patience and professionalism. They greet every voter, the grateful and the grumbling alike, with dignity. They absorb frustration that is not theirs to bear and they do not waver. And while they represent their party, when you get to know them as I have, you know they are doing it for their country and community. They understand the gravity of the work, and the gift they have been sworn to protect.
"They are a rare breed, and I couldn't be prouder of Petter and his fellow election judges. McHenry County is truly blessed by these stalwart patriots.
"They do not do this for the pay. They do not do it for recognition. They do it because they are the kind of people who still believe that showing up matters, and that civic duty is not a burden but a privilege.
"What Petter Culver did - what all our election judges do - is among the most profoundly patriotic acts available to a private citizen. They are the quiet guardians of the ballot box. They are the human infrastructure of liberty itself.
"To every election judge serving McHenry County: we appreciate you. We honor you. What you do is sacred work.
"And to Petter, who gave his last full measure of devotion not on a battlefield, but at a polling place in the community he loved, we say thank you. You did not just talk about democracy. You showed up for it, right until the very end.
"Rest now, Petter. Your work here is done, and it was done well.
"We'd like to share a special word of thanks the McCullom Lake Police Department, and Coroner Dr. Michael Rein's office, for their cooperation and support during this tragedy."