Mariana County is one of the named counties of the fictional State of Leonida, the setting for Grand Theft Auto VI. Confirmed only briefly through environmental signage in the game's second trailer, the county nevertheless occupies a strategically significant position in the southern portion of the state, where its territory is understood to envelop two of the game's most prominently marketed regions: the swampy Grassrivers and the tropical Leonida Keys (GTA Wiki, 2026a). Because Mariana County remains an "upcoming content" entity at the time of writing, every claim about it must be filtered through the dual lenses of confirmed trailer evidence and reasoned inference drawn from adjacent, better-documented locales. This report compiles what is known, what is reasonably inferred, and what remains speculative regarding the county, drawing on the GTA Wiki entries for Mariana County itself, the Leonida Keys, and the Grassrivers, each of which corroborates the others. The intent is to provide a defensible baseline against which future trailers, the game's launch and post-launch documentation can be measured.
Mariana County occupies the southern flank of the State of Leonida, the GTA VI analogue of the U.S. state of Florida (GTA Wiki, 2026a). Its boundaries are not fully delineated in trailer-era materials, but the county is documented as encompassing both the Grassrivers wetlands and the Leonida Keys archipelago (GTA Wiki, 2026a; GTA Wiki, 2026b). The Grassrivers — a flooded grassland inspired by the Everglades and partly named after Marjory Stoneman Douglas's 1947 work The Everglades: River of Grass — straddles Vice-Dale County to the north and Mariana County to the south, suggesting that Mariana County's northern frontier traces through swampland rather than along any urban edge (GTA Wiki, 2026c). To the south, Mariana County terminates in the Leonida Keys, an archipelago that forms the southernmost extremity of the continental United States within the game's geography and which is reached via the Keys Causeway from southern Vice-Dale County (GTA Wiki, 2026b). Two settlements have so far been associated with the county: Key Lento, in the Keys, and Watson Bay, a Grassrivers-adjacent town (GTA Wiki, 2026a). The county is also said to neighbour Kelly County, home of Port Gellhorn, on the basis that an Interstate 404 sign in Port Gellhorn named Mariana County as a destination (GTA Wiki, 2026a).
The defining piece of canonical evidence for Mariana County is a roadside Interstate 404 sign visible at 2:28 in the second GTA VI trailer, situated within Port Gellhorn and listing Mariana County alongside Vice-Dale County as a forward destination (GTA Wiki, 2026a). This single sign is what confirms the county's existence and its place in Leonida's interstate routing. Beyond that, Mariana County is documented indirectly through the promotional website's location postcards: the Leonida Keys postcard explicitly identifies the archipelago as situated within Mariana County, while the Grassrivers postcard, by acknowledging the wetland's reach into the south, implies the county's swampland character (GTA Wiki, 2026b; GTA Wiki, 2026c). Trailer screenshots additionally show the Keys in panoramic aerial shots and an airboat traversing the Grassrivers, both of which can now be retrospectively understood as Mariana County footage (GTA Wiki, 2026b; GTA Wiki, 2026c). Hurricane Roxy, an in-game weather event referenced in promotional materials for the Keys, is implied to have struck this region before the playable narrative begins, hinting that storm damage may be a recurring environmental motif within the county (GTA Wiki, 2026b).
Given Mariana County's real-world analogue — Monroe County, Florida — several reasonable inferences follow (GTA Wiki, 2026a). Monroe County is geographically unusual in that the bulk of its land area lies within the Everglades on the mainland, whereas the bulk of its population sits offshore in the Florida Keys; this asymmetry is likely to be replicated in Mariana County, with Watson Bay representing a thinly populated mainland community and Key Lento (alongside other yet-to-be-revealed keys) representing the more developed tourist economy. The Leonida Keys's promotional tagline — "Gateway to Paradise … the dress code is casual, the bars are loaded" — strongly suggests a Key West analogue at the chain's terminus, with the associated leisure economy, dive tourism, and maritime smuggling possibilities that have long characterised Rockstar's southern Florida pastiches (GTA Wiki, 2026b). Conversely, the Grassrivers's marketing copy — emphasising "deadlier predators" and "weirder discoveries among the mangroves" — combined with the GTA IV-era Leftover-vacations.com description of the area as a "swamp full of right-wing nutjobs and deadly mosquito-born diseases" suggests that the mainland portion of Mariana County will host themes of paramilitary subculture, fringe politics and ecological menace (GTA Wiki, 2026c). It is plausible, though unconfirmed, that Mariana County will serve as a low-density playground for water-based traversal (airboats, sport fishing vessels, light aircraft), in counterpoint to the dense urban gameplay loop expected of Vice City within Vice-Dale County.
Mariana County is, on the evidence available, a southern Leonida county built around two contrasting biomes: the mangrove-and-marsh Grassrivers along its northern reach and the tropical Leonida Keys at its southern tip, with Watson Bay and Key Lento as its identified settlements (GTA Wiki, 2026a). It draws directly on Monroe County, Florida, and represents Rockstar's most explicit recreation yet of the Florida Keys and Everglades within the HD Universe. Whilst the county's full extent, its administrative seat, its road network beyond Interstate 404, and its mission relevance to protagonists Jason Duval and Lucia Caminos remain unknown, the trio of associated regions — Mariana County, the Grassrivers, and the Leonida Keys — collectively form a coherent southern leisure-and-wilderness sandbox that contrasts sharply with the urban density implied for Vice City to the north. Further trailers and the game's eventual release in 2026 will be required to confirm the county's internal subdivisions, its position relative to the bay islands south of Vice City, and the degree to which its swampland and island portions are connected by playable infrastructure.
GTA Wiki (2026a) Mariana County. Available at: https://gta.fandom.com/wiki/Mariana_County (Accessed: 14 May 2026).
GTA Wiki (2026b) Leonida Keys. Available at: https://gta.fandom.com/wiki/Leonida_Keys (Accessed: 14 May 2026).
GTA Wiki (2026c) Grassrivers. Available at: https://gta.fandom.com/wiki/Grassrivers (Accessed: 14 May 2026).
Rockstar Games (2025) Grand Theft Auto VI — Trailer 2. Rockstar Games promotional release. Referenced via GTA Wiki (2026a).
Rockstar Games (2025) Grand Theft Auto VI — Promotional Website: Leonida Keys and Grassrivers postcards. Available at: https://www.rockstargames.com/VI/ (Accessed via secondary documentation in GTA Wiki, 2026b; 2026c).