Police arrested more than 300 Occupy protesters Oct. 16 and Oct. 23 in 2011 for violating the curfew at Grant Park. At the time, Chicago Mayor Rahm Emanuel considered the arrests a model for how to maintain order while respecting protesters' rights.
Associate Judge Thomas Donnelly, though, threw out the charges against 92 of the protesters, the Chicago Tribune reported.
Donnelly said his ruling was based on the fact that the city routinely did not enforce the curfew law for events it supports, like the 2008 rally on the night Barack Obama won the presidency.
"We're incredibly pleased by Judge Donnelly's ruling. This is a significant First Amendment ruling for the Occupy protesters, and all Chicagoans," said lawyer Thomas A. Durkin, who represented 12 University of Chicago students.
Durkin said it was unclear whether Thursday's ruling would affect the cases of more than 200 protesters who took court-supervision offers in exchange for avoiding a conviction on their records.