Google is your friend. Sumter county's ordinances are all online.
You can
read the animal control rules here
They include:
Direct control shall mean immediate and continuous physical control of an animal at all times such as by means of a fence, leash, cord, or chain of sufficient strength to restrain the animal; or in the case of specifically trained working, agricultural or hunting animals which immediately respond to such commands, while working; direct control shall also include aural or oral control, if the controlling person is at all times clearly and fully within the unobstructed sight and hearing of the animal.
and
No person shall cause, permit, or allow a dog or cat to stray or in any manner to run at large [not under direct control as defined above] in or upon any public street, sidewalk, or other public property or the property of another.
So to answer the OP's question.. No dog or cat can be at large. A dog does not have to be on a leash but does have to be under the direct control of a nearby person.
Other rules include:
All cats must have a license and a rabies vaccine tag, not just dogs and ferrets.
No animal in heat may be outdoors.
Any cat which is not sterilized cannot be outdoors unattended. No exceptions.