The Arab League peace plan called for Syrian President Bashar Assad to step down.
The U.S., Britain and France were among the Security Council members voting in support of the measure.
The vote took place as Syrian forces pummeled the city of Homs with mortar and artillery fire.
Activists say the attack killed more than 200 people in one of the bloodiest episodes in the uprising against President Assad.
The group 'Answer Chicago' organized the local rally. One member said the biggest threat to peace in the Middle East are the actions of the U.S. government.
The protestors said they were taking a stand for peace and justice.
Organizers said similar rallies were planned today in 70 cities around the world.
