Mutsu Munemitsu
As a minor coastal settlement, Ōiso was under the control of the later Hōjō clan of Odawara during the Sengoku period. In the Edo period, it was nominally part of Odawara Domain, and developed as Ōiso-juku, a post town on the Tōkaidō connecting Edo with Kyoto. After the Meiji Restoration and with the establishment of the district system in 1878, it came under the control of . Ōiso became a town on 1 April 1889 with the creation of the modern municipalities system. Blessed with a temperate climate, and with convenient access to Tokyo due to the Tōkaidō Main Line railway, it was favoured as a seaside health resort by politicians and literary figures during the Meiji period after a glowing report on its location was written by noted physician Matsumoto Jun. Prime Minister Itō Hirobumi, Yamagata Aritomo, Saionji Kinmochi and Ōkuma Shigenobu, Foreign Minister Mutsu Munemitsu, writer Shimazaki Toson and "zaibatsu" founder Yasuda Zenjirō had summer residences in Ōiso. This popularity continued into the postwar era, and Prime Minister Shigeru Yoshida also had a residence in Ōiso to which he retired after leaving politics. The former Itō, Yoshida and Shimazaki residences have been preserved as memorial museums.