Here's a lengthy Fox News write-up from last year.
On Sept. 27. 1986, more than 100,000 people filled Public Square in downtown Cleveland for the charitable event.
Balloonfest ’86 was a fundraising event sponsored by the United Way and included [a] legendary balloon artist ... from California.
“The United Way and they’re going to put Cleveland back on the map. They’re gonna have a giant balloon launch,” said FOX 8’s [reporter], who also covered the event.
It took months of planning and thousands of volunteers to inflate the 1.5 million balloons that were to be released. They were held in place by a specially constructed netting structure.
Here's a short documentary by the Atlantic, (appropriately) cut like a found footage horror movie. It was directed by Nathan Truesdell, art director on "You're Next."