The Sakaisawa Documents are a collection of over 5,000 documents passed down through the Sakaisawa family, who served the Tamura family of the Ichinoseki Domain, a branch domain of the Sendai Domain, during the early modern period.

The Sakaisawa family, who resided in Sakaisawa Village, Kadota-sho (present-day Aizu, Fukushima Prefecture) during the medieval period, adopted the name Sakaisawa and served the Ashina clan. After the fall of the Ashina clan, they became vassals of the Date clan and later became retainers of the Tamura family.

The Tamura family was the birthplace of Masamune's wife, Aihime, and was revived by Muneyoshi, the third son of the second lord of the domain, Tadamune, after the family name had died out. In 1660, they became an internal daimyo by being granted 30,000 koku from the 620,000 koku of the Sendai domain, and in 1681, they established their base in Ichinoseki.

The heads of the Sakaizawa family throughout history have all served as Omotogashira (head of the shogunate's bureaucracy), with the first and second generations serving as Omotogashira. From the third generation, Kihei Morisada, onwards, they have held positions such as town magistrate and Honshime (responsible for managing finances), as well as serving as Goyonin (official in charge of the shogunate's bureaucracy) and Gokaro (chief retainer), making them high-ranking vassals.

The Sakaizawa documents contain related papers, ledgers, and notes accumulated during the tenure of each official, offering insights into the duties of those in office as well as the state of the domain's administration. In addition, the collection includes a wide variety of documents, from household records that offer a glimpse into the lives of samurai, such as those concerning weddings and funerals, and letters between family members, to documents related to scholarship and martial arts. This collection of documents provides valuable insights into the public and private lives of high-ranking samurai in the early modern period.