All of Rockstar's GTA states have been divided into counties - GTA V divided San Andreas into Los Santos County and Blaine County. Leonida almost certainly follows suit, but Rockstar hasn't published it.
This article is explicit conjecture - we infer a county system from the visible regions, and we say so plainly. If you're looking for confirmed material, stick to the Leonida hub.
Why a county structure probably exists
Two reasons. Firstly, Rockstar's convention - GTA V used counties for navigation, narrative and aesthetic reasons. Secondly, real-life Florida is heavily county-organised, and GTA 6 draws inspiration from real-life Florida. The game will probably ship with at least two named counties.
It is unknown whether counties are represented as text labels on the in-game map (the GTA V pattern) or only appear as background flavour.
A working county breakdown
One county for Vice City and the surrounding suburbs (analogous to Miami-Dade). One county for the swamps and small towns further inland (analogous to Collier, or a combined Everglades county). One county for the Keys (analogous to Monroe). Maybe a fourth county for the more northern inland areas.
All of this is completely speculative. None of it has been officially published or named by Rockstar. We hedge accordingly.
Why this matters
Mechanically, it likely does not. Counties in GTA are mostly cosmetic - influencing signage, radio chatter, and police jurisdiction only in narrow ways. They're meaningful on the map, but not gameplay-wise.
The bigger reason this article exists: many members of the community confidently use 'Leonida county names' that have never come from an official source. We try to be transparent about which is official and which isn't.