Also known as International Workers' Day, the public holiday, observed on May 1, commemorates the work of unions and pro-labor groups.
Its origin is deeply rooted in the history of Chicago's labor movement.
In 1886, thousands of industrial workers went on strike, leading to the events at Chicago's Haymarket.
The 3.1-mile course starts and ends at the Chicago Firefighter and Paramedic Memorial Park.
The May Day 5K Run and Walk began at 8 a.m.
Money raised from Sunday's event will go toward the Chicago Federation of Labor's ongoing efforts to support workers in Chicago and across Cook County.