Chiba Prefecture Onjuku has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

The pines and sand of Ajiro Bay in Onjuku were referenced in a poem by Hōjō Tokiyori (1227–1263), a Kamakura-period administrator.

One of the survivors was Governor General of the Philippines Rodrigo de Vivero, who was subsequently granted an audience with shōgun Tokugawa Ieyasu.

[4] In 1928 a tower was built in Onjuku to commemorate the landing of Rodrigo and friendly relations between Mexico, Spain, and Japan.

It has since been designated a Prefectural Historic Monument (県指定史跡 (ken shitei shiseki)), and is surrounded by an extensive garden complex.

Onjuku has a mayor-council form of government with a directly elected mayor and a unicameral town council of 12 members.

In terms of national politics, the town is part of Chiba 11th district of the lower house of the Diet of Japan.

The sandy beaches of Onjuku are the representative swimming areas of the Sotobōsō Coast and attract numerous tourists during the summer months.