Monterey Pop is cited as being the grand daddy of these festivals although there was one in SF the week before Monterey Pop and there were the Newport jazz and folk fests before that.
There were a lot of these fests in 1969 before and after Woodstock, with a number of the same acts.
I never went to any of the big fests, but saw a lot of great acts in HS in Kiel Auditorium in St Louis and a small venue in Creve Coeur. I think my tinnitus was caused by all those shows.