Odawara Domain
During the Edo period, the area around present-day Nakai was part of Odawara Domain in Sagami Province. After the Meiji Restoration, it became part of Ashigarakami District in Kanagawa Prefecture. Nakai village was formed on April 1, 1889 with the establishment of the modern municipalities system. It merged with neighboring Iguchi village on April 1, 1908. The village was elevated to town status on December 1, 1958.