This weekend is the second North Michigan Ave Arts Festival of the summer, the first being a few weeks ago and couple blocks south called the Millennium Art Festival.
This one is actually called the North Michigan Arts Festival and is July 5th, 6th, and 7th: Fri-Sat 10AM to 6PM and Sun 10AM to 5PM.
It is at Pioneer Court which is just north of the river on Michigan Ave. It is the plaza in front of the Equitable Building, next to the Tribune Tower i.e. across from the Wrigley Building.