Humans first settled the area that is now Setagaya an estimated 30,000 years ago, in the Paleolithic period.  127 sites dating from the Jomon Era (about 2,000-12,000 years ago) have been found in the city‘s heights, and 20 site dating from the Yayoi Era (about 2,000 years ago), when rice cultivation began, have been confirmed.  The oldest historical reference to Setagaya dates from the 14^th century (Kamakura Era), where it is noted as the site for a territorial battle between the Kitami and Kumagai clans.  In the Muromachi Era (1336-1573) Setagaya became the territory of Oshu ( in present-day Tohoku) under the deputy-ship of the Kira family; in the 16^th century it came into the hands of the Odawara Hojo family.  It was around this time that the Hojo family created an open market in the post town of Setagaya Shinjuku; this was the original Boro-ichi flea market.  With the establishment of the Tokugawa Shogunate, the territory of Setagaya came under Ii family rule as part of the Hikone Domain (in modern-day Shiga Prefecture).  The shogunate concentrated its efforts on irrigation projects, completing an aqueduct that flowed from the Tama River, and, later the Karasuyama other irrigation canals.  These projects dramatically increased the amount of irrigated land in Setagaya.

  After 1913, huge numbers of Tokyo victims of the Great Kanto Earthquake had resettled in Setagaya.  The completion of new railways encouraged further migration to the area; by 1930, Setagaya’s population had swollen to 150,000 from its 1920 level of 40,000, transforming what had been a purely rural area in the Edo and Meiji eras.  In October 1932, four towns ? Setagaya-machi, Komazawa-machi, Tamagawa-mura, and Matsuzawa-mura ? were incorporated into Tokyo City.  Four years later, with the addition of Kinuta-mura and Chitose-mura, Setagaya reached its modern proportions.