The county handles permitting for all unincorporated areas, while the cities of Kissimmee and St. Cloud operate their own independent building and zoning departments. Development within the county is subject to the Osceola County Land Development Code, which includes specific requirements for the Urban Growth Boundary and various environmental overlays including floodplains and wetlands.
How this fits with the state
The state authority here is Florida DBPR - Construction Industry Licensing Board. The county file does not replace that — it adds the permit office, local overlays, and the actual filing path.