As far as I know, and I'm open to correction, there has only been 10 deaths in the history of Disneyland. One of those being the one at the Disneyland Resort which was suicide and I'm not sure if it counts. Only 2 of them were actually Disney's responsibility. That's almost 53 years and they can still count them on both hands. That is pretty damn impressive. I can't vouch for Disneyworld though. I know they have a pretty high mortality rate in the water parks.
I think Six Flags has that many in the last 10 years.