Isumi is a city located in Chiba Prefecture, Japan. As of 1 November 2020, the city had an estimated population of 37,206 in 17,004 households and a population density of 240 persons per km2. The total area of the city is 157.44 square kilometres (60.79 sq mi).

Kujūkuri Beach is a sandy beach that occupies much of the northeast coast of the Bōsō Peninsula in Chiba Prefecture, Japan. The beach is approximately 60 kilometres (37 mi) long, making it the second longest beach in Japan. Kujūkuri Beach is a popular swimming and surfing destination for inhabitants of Greater Tokyo. The beach is protected as part of Kujūkuri Prefectural Natural Park.