A parade was also scheduled. Mayor Rahm Emanuel, Republican Gov. Bruce Rauner and many candidates running in Tuesday's primary election were expected to march.
The grand marshal is Alderman Patrick O'Connor. He says it's a chance to celebrate "the hard working Irish men and women" of Chicago.
The Chicago Plumbers Union started the tradition of dyeing the river green, with a material once used to locate leaks in buildings. Organizers say the powder used is a secret recipe and is environmentally safe.