Event organizers estimated that 250,000 attended the rally, but city officials did not immediately release a crowd estimate. Attendance was three times what was expected and was among the largest outside the marquee Women's March on Washington event.
"We are a movement. It's like we're not going to be stopped," said Elaine Spicer, who attended the Chicago event.
"We want people who connect, protect but activate is the key word in our motto," said event co-chair Ann Scholhamer.
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The rally started at 10 a.m. in Grant Park at the intersection of Columbus Drive and Jackson Boulevard. Speakers included Illinois Attorney General Lisa Madigan, Cook County President Toni Preckwinkle, Aldermen Pat Dowell, Susan Garza and Michele Smith and others. Members of the Chicago cast of "Hamilton," also spoke and then sang "Let it Be."
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A march to Federal Plaza in the Loop was canceled as the streets were filled with people. Despite the cancellation of the official march, many made their way to Federal Plaza anyway while the rally was going on.
The Grant Park rally ended after 1 p.m., but demonstrators in pink hats and signs continued to litter the streets for hours.
Many men were also in attendance in Chicago, and elsewhere.
"It's about moving forward with an agenda for the future as opposed to trying to roll back to policies that didn't work in the past," said Ernest Sullivan, a demonstrator in Chicago.
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The Chicago Office of Emergency Management and Communications said: "While there was no longer an official pedestrian march facilitated by the organizers, the Chicago Police and supporting City agencies worked to ensure the safety of some participants that took to the streets for a spontaneous march. The event and ensuing march were peaceful and with limited disruption."
Whitney and Elliot Michel were among the thousands in Grant Park for the rally.
"I think it's important to take advantage of an event like this that gets you off of your computer and Facebook complaining about issues and coming out here and being reminded that there are people that share your values and they're out here to make a stand to show that they are here and to show that they care," said Whitney Michel.
"It's very important for us to stand up for rights of under-served groups. I think women are a vastly under-served group. I have a wife, I have a mother, I have two sisters. Many of my students are young women and they deserve all of their rights," said Elliot Michel.
Friday night, city workers began installing fences and barricades to outline the march route and keep people safe.
On what inspired the march, organizer Jessica Scheller said. "It's about more than the election of the president, it's about the mindset which led to his election."
Saturday morning, marchers were putting finishing touches on posters and getting signed in, all in preparation of sending a big message.
"Our mission is to eliminate racism and empower women. I feel so inspired to be a part of this committee and work with these women to fight for the rights of women," said Jacqueline Priego, part of the planning committee for the Women's March on Chicago.
March organizers said they are well aware of the potential trouble and expect this march to be peaceful, but they are taking no chances by having additional security.
"Because the numbers have grown so much, our logistics have changed a few times, so with that we've been in constant contact with the Chicago Police Department as well as the city and moving the location of the stage to ensure that we do not have any issues and I think with additional fencing that we added early this morning at 3 a.m. We're ready to go," said organizer Danica Milich.
This march in Chicago was one of about 600 that happened around the world Saturday, including in Washington D.C. where hundreds of thousands marched.