Don't know what county Universal is in, but Disney is definately in Orange County...
... EXCEPT the All-Star Restorts, which are in Osceola.
I only remember this because someone once posed the question on these boards as to why they paid a different sales tax in one part of Disney as to another. So someone dug out a map and found that the border of the two counties cut across the bottom corner of the resort.
Anyway - in Orange County, sales tax is 6.5% on goods, 11.5% on hotel rooms, while is Osceola it is 7% on goods and 12% on rooms.