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"We will shut you down, we will cite you, and if we need to, we will arrest you and we will take you to jail," she said Saturday during a press conference.
Lightfoot said Chicago police broke up gatherings of between 50 and 150 people on Friday night, and that authorities were tipped off to at least six parties and gatherings that were set for Saturday night, ABC 7 reported.
"This frankly doesn't come as a surprise, given the warm weather. We've all been cooped up. We all miss our friends, and we all want to go outside and gather in groups," Lightfoot said. "However, those aspirations simply cannot become a reality in the middle of a pandemic."
"If you host a party, promote a party, or go to a party, we are not playing games. We mean business, and we will shut this down one way or another," she said, NBC Chicago reported. "The time for educating people into compliance is over. Don’t be stupid. We’re watching you, and we’re going to take decisive action."
As of Saturday afternoon, Illinois had the fourth most coronavirus cases in the U.S. with more than 56,000 and the sixth most deaths with nearly 2,500.
Fox News' Danielle Wallace contributed to this report