A woman identifying herself as Mayor Steve Chirico's niece called out the family on Twitter for attending, saying "I actually don't need to protect these people, because they don't think they've done anything wrong."
Chirico said Sunday his entire family tested negative for COVID-19 before the trip, adding it was an outdoor event with 53 people.
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The mayor said he will get tested again and quarantine when he gets back to west suburban Naperville to follow state guidelines.
Gov. JB Pritzker is urging Illinoisans to stay home as COVID-19 cases continue to surge across the state and much of the country.
Naperville is part of DuPage County, which recently fell below the hospital bed availability target the state has established. The county is working to expand COVID-19 testing, as well.