When I was younger the downtown Chicago St. Patrick's parade was held on St. Patrick's Day, no matter what day of the week it was. Not a lot of work was done and a lot of businesses were closed...but the pubs were always open. 
Now the downtown parade is the Saturday before March 17th, and the South Side Irish parade is the Sunday before. After mass. Always.
Now the downtown parade is the Saturday before March 17th, and the South Side Irish parade is the Sunday before. After mass. Always.