The Midwest Rock Festival took place at State Fair Park in West Allis, Wisconsin (suburb of Milwaukee), on July 25-27, 1969.

A huge lineup of acts  played to a relatively small audience of 25,000.  The show had a flatbed trailer as a stage set on the field in front of the racetrack grandstand.  A poster from the show went for $1,500!  The following is a list of performers who were advertised to come, but not all did:

• Delaney and Bonnie and Friends (including Eric Clapton)
• Blind Faith
• Jethro Tull
• Johnny Winter
• The First Edition
• Taste with Rory Gallagher
• Joe Cocker
• Buffy Sainte-Marie
• Jeff Beck
• Pacific Gas & Electric

According to Wikipedia, these are the acts that did appear on July 25:

• Led Zeppelin
• Buffy Sainte-Marie
• The First Edition
• Sweetwater
• Pacific Gas & Electric
• SRC
• Shag

July 26:

•  Blind Faith
• Delaney and Bonnie and Friends
• Shag
• Taste
• John Mayall & the Bluesbreakers
• MC5

July 27:

• Johnny Winter
• Joe Cocker and the Grease Band
• Bob Seger System
• Jim Schwall Blues Period
• MC5
• Zephyr
• Shag
• Litter
• SRC

Tom on Facebook reported that:

Show ended early on the third day when Jeff Beck took the stage and announced checks were bouncing and groups weren’t getting paid, said “Fxxx It!” and walked off without playing. Then Johnny Winter came on and said he heard the same news, said “Fxxx It!” and played for two hours to close out the festival.