Susan asked: Is it illegal to ride bikes on sidewalks in Seminole County?
Unless there is a local ordinance to the contrary, it is legal to ride bicycles on sidewalks in Florida.
s. 316.2065 – Bicycle Regulations
(9) A person propelling a vehicle by human power upon and along a sidewalk, or across a roadway upon and along a crosswalk, has all the rights and duties applicable to a pedestrian under the same circumstances.
(10) A person propelling a bicycle upon and along a sidewalk, or across a roadway upon and along a crosswalk, shall yield the right-of-way to any pedestrian and shall give an audible signal before overtaking and passing such pedestrian.
I found no local ordinance that prohibits sidewalk cycling in Seminole County. You can see the code of ordinances here:
You should also check your municipality code for such ordinances or call your local police.