It is bordered by the Pacific Ocean to the east, and enjoys a temperate maritime climate, with short, cool winters and hot, humid summers due to the effects of the Kuroshio Current offshore.

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

The place name is very ancient, appearing even in the Nihon Shoki, which mentions the area as the source of abalone and pearls for the Yamato court during the reign of the Kofun period Emperor Ankan.

Isumi has a mayor-council form of government with a directly elected mayor and a unicameral city council of 18 members.

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

Ise-ebi, a species of spiny lobster, is a notable product of Isumi, as are sardines and Japanese amberjack.

The border between Ichinomiya and Isumi City starts at the southern end of the 60-km Kujūkuri Beach adjacent to Taito port.