Trumbull Valley is the map featured in the original State of Decay campaign, as well as in the Breakdown DLC. Located in the north/northwestern United States and boasting a wide area with gently rolling hills, rivers, and mountains on all sides, Trumbull Valley contains a rich assortment of settlements and points of interest. It is, however, unfortunately overrun by zombies for the entire duration of the game.
Trumbull Valley was formed during the last major ice age millions of years ago, as water flowing down from Canada brought rich silt and soil, depositing them in the floor of the valley. Shielded by the mountains that ring the valley and fed by nutrient rich soil from glacial run-off, the valley was perfect for farming.
Native American Indian legends surrounded Trumbull Valley since its discovery. Stories about beasts in its lakes and rivers, as well as spirits that roamed the valley and its forests were well-known by all in the region. The legends persist even in the modern day, as native locals speak of voices from the hills and the cries of long-dead ancestors.
The arrival of settlers heading west marked the beginning for Trumbull Valley's modern history. Farms were built in the center of the valley atop the fertile soil, and the towns of Marshall and Spencer's Mill were established in the southern and northern parts of the valley, respectively. Spencer's Mill in particular took advantage of the lush woodlands that cover the northern half of the valley, while Marshall became the metropolitan seat in Trumbull.
The settlements and areas of Trumbull Valley are connected by US Route 406 that circles the valley perimeter. This road enables locals and visitors to make a complete circuit of the valley from the comfort of the road.
The Valley is divided into six rough sections by the locals:
Part of the rough mountain ranges that form the Valley's northern border, Mt. Tanner is home to a national park and ranger station. It is a popular campground, known for its fishing and hunting. Few "modern" buildings exist in the area; only the Ranger Station, a gazebo, and a restroom building are part of the park complex. A small number of cabins, rented out by the park service, are scattered around the area.
Located in the northern part of the valley, Spencer's Mill is a small community on the edge of the northern mountains and woodlands. The town has few notable structures, although it is home to the Church of the Ascension and the Fork in the Road Diner. A gun store, veterinary clinic, and post office are also present in town, as is a Swine & Bovine restaurant. A large collection of houses and a trailer park are also present in town.
The Valley's main metropolitan center, Marshall is a large town straddling a river at the far southern end of the valley. Bordered by a river to its north and rugged mountains to the south, Marshall is nevertheless a significant town, with a main street any American town would be proud to have. The County Court House forms the seat of local government and is situated in east Marshall, next to a picturesque park along the river that divides the town.
East Marshall is largely commercial and residential property, while west Marshall is more industrial.
Located across the river that forms the western border of the valley, Fairfield is the site of the Trumbull County Fairgrounds. Sparsely populated, Fairfield is largely flat and, apart from the fairgrounds, has no noteworthy landmarks.
The center of the valley, surrounded by the loop road, is given over to farming. Sprawling fields cover the bulk of the valley floor, dotted by barns and farmhouses, with the occasional windmill nearby. Orchards are also found along the southern and southwestern edges of the valley.
A large concrete dam, apparently of the double wall construction type, located very close to the town of Fairfield. A road, inaccessible until the endgame, runs along the top of the dam, but is blocked by a military barricade. The dam creates a sizable reservoir to the northeast, forming part of Fairfield's northwestern border. The large, metropolitan city of Danforth is visible from the dam.
In the wake of events that led to the zombie uprising, Trumbull Valley has been nearly completely depopulated. The woods of Mt. Tanner and the town of Marshall are particularly dangerous, infested with undead of all descriptions.
Small pockets of survivors continue to hold out, however, and maintain settlements within Spencer's Mill, Marshall, and various outbuildings around the valley.
The US Army were stationed in Fairfield as part of Operation: Washout and additionally,there was another operation being run under the name of 'Boxtop'. Later on, Operation: Boxtop was abandoned and all personnel of the operation were evacuated from Trumbull Containment Barrier. Just before Fairfield becomes a playable area, Captain Monstressor gets angry at Sgt Tan for not leaving a civilian to die and gets all the remaining personnel to evacuate. This results in Fairfield being abandoned and Sgt Tan being left for dead with the other survivors. However, when they blow their way into Fairfield, it was heard from outside between Danforth and Trumbull Valley and reported. No scouts were available at the time so the Army did not know about what went on. When the player eventually escapes, there are reports of the explosion from the vicinity of Trumbull Valley which may mean there are still Military Soldiers stationed in the surrounding area apart from Danforth So The Area Is Infested With Plauge Zombies.