Much of Dewa Province was controlled by the powerful Mogami clan during the Sengoku period. The Mogami established a subsidiary holding centered on Sakanobe Castle in what is now Mamurogawa in Yamagata, based on the Sengoku-period foundations of a structure erected by the Onodera clan. However, the Mogami were dispossessed by the Tokugawa shogunate in 1622, with the majority of their holdings going to the Satake clan, who were transferred from Hitachi Province to their new holdings at Kubota Domain. Tozawa Moriyasu, a relatively minor daimyō originally from Kakunodate in Dewa Province served Toyotomi Hideyoshi at the Battle of Odawara in 1590; however, he fell ill and died shortly thereafter. His son, Tozawa Masamori sided with Tokugawa Ieyasu at the Battle of Sekigahara, and was eventually promoted to the status of a 40,000-kokudaimyō at Hitachi-Matsuoka Domain in Hitachi Province. When the Mogami were dispossessed, the Tokugawa shogunate transferred him from Hitachi to the newly created Shinjō Domain, and increased his revenues to 60,000 koku, where his descendants ruled for 11 generations to the Meiji Restoration. In 1625, due to development of new rice lands, the domain's official revenues were increased to 68,200 koku. Masamori died in 1650, and his son Tozawa Masanobu ruled for the next 60 years, providing the domain with an exceptionally long period of stability and prosperity. Its actual revenues in the Genroku era were estimated at 132,000 koku, and its population approached 60,000 inhabitants. However, towards the end of Masanobu's era, and under his son Tozawa Masatsune, the domain suffered severely from lax taxation and fiscal policies, and repeated crop shortages in the Hōei, Tenmei and Tenpyō eras. From the 5thdaimyō, Tozawa Masanobu through the 10th daimyō, Tozawa Masayoshi, the domain attempted to implement fiscal austerity policies, and to introduce new sources of revenue, but with little effect in removing the deep debt burden on domain finances. During the Boshin War of the Meiji Restoration, Shinjō Domain was initially in favor of the Satchō Alliance, but later became a member of the Ōuetsu Reppan Dōmei. However, after Kubota Domain switched sides to favor the Meiji government, Shinjō Domain soon followed. Neighboring Shōnai Domain, outraged by the betrayal, sent its army to invade Shinjō Domain, and after a fierce battle, destroyed Shinjō Castle and much of the surrounding castle town. The 11th daimyō, Tozawa Masazane escaped to Kubota Castle, where he remained in exile for 70 days until his domain was liberated by forces loyal to the new Meiji government. On June 2, 1869, the new government awarded Shinjō Domain with an increase in revenues of 15,000 koku. However, later the same month, the government issued a decree abolishing the domain system. The former domain was absorbed into Yamagata Prefecture in July 1871.
