The Sayama Domain (狭山藩 Sayama-han) was a Japanese domain of the Edo period, located in Kawachi Province, and headquartered in what is now Ōsakasayama. It was ruled for the entirety of its history by the Hōjō clan, a branch of the Late Hōjō clan.
The Late Hojo Clan was started by Hōjō Sōun and at its zenith during the Sengoku period controlled all of the Kanto region. However, its power attracted the attention of Toyotomi Hideyoshi and when they failed to heed a summon to submit to Hideyoshi at his castle in Osaka, Toyotomi roused a great host numbering 200,000 and laid siege to Odawara Castle. After the fall of the castle, the Hojo lord's father Hōjō Ujimasa and his uncle Hōjō Ujiteru were forced to commit Seppuku while the young lord Hōjō Ujinao was exiled to Mount Kōya. However, the family line did not die there, Hōjō Ujinori a younger brother of Ujimasa developed a deep friendship with Tokugawa Ieyasu when they were both hostages to the Imagawa family. After the disbanding of the Hojo Domain, Ujinori obtained a 10,000 koku stipend from Ieyasu. He bequeathed 4,000 koku to his son Hōjō Ujimori and Ujimori was adopted by Ujinao to symbolically continue the family line of the Late Hojo family.