The Eagles were at the Mississippi River Festival on July 17, 1974, which was sponsored by Southern Illinois University in Edwardsville, IL. This was an annual festival, and the Eagles were also at the MRF in 1975 and the Spring Fest in 1973. The first concert at the MRF was in 1969, and the last was in 1980. Both symphonies and rock concerts were held there under the big tent. A Mississippi River Festival 40th anniversary video talking about the history of the MRF is on the Festivival page.
This was a double-bill concert with Joe Walsh and his band, Barnstorm.
1974 Photo used in advertisement below
Randy Meisner, Glenn Frey, Don Henley (on drums), and Don Felder
Advertisement later used for Mississippi River Festival in Edwardsville, IL
Eagles photo in this ad is from this July 17, 1974 performance
Eagles at Mississippi River Festival 1974
Page below is a page from Focus magazine (Southern Illinois University of Edwardsville quarterly magazine)
October 1974 issue
The bottom-right photo of the three was taken in the spring of 1973 while the Eagles were at Southern Illinois University for the Spring Fest on May 25, 1973. It was included on this same page with the other two photos but was taken by a different photographer.
St. Louis Post-Dispatch (St. Louis, MO) – June 30, 1974
Mt. Vernon Register-News (Mt. Vernon, IL) – July 10, 1974
Alton Telegraph (Alton, IL) – July 18, 1974
Doug Thompson doesn’t seem to be a Joe Walsh fan.
St. Louis Post-Dispatch (St. Louis, MO) – July 18, 1974
Alton Telegraph (Alton, IL) – Aug. 17, 1974