Isogo-ku (磯子区) is one of the 18 wards of the city of Yokohama in Kanagawa Prefecture, Japan. As of 2010, the ward had an estimated population of 163,406 and a density of 8,520 persons per km². The total area was 19.17 km². Isogo is located in eastern Kanagawa Prefecture, and in the southeast corner of the city of Yokohama. The area is largely flatland, with scattered small hills. The Ward is bordered to the east by Tokyo Bay.
During the Edo period, area around present-day Isogo Ward was formerly part of the tenryō territory in Sagami Province controlled directly by the Tokugawa shogunate, but administered through various hatamoto. The area consisted of small fishing villages, noted primarily for their catch of Sea cucumber. After the Meiji Restoration, the area became part of Kuraki District in the new Kanagawa Prefecture. In the cadastral reform of April 1, 1889, the area was divided into numerous villages. On April 1, 1901 Negishi village was annexed by neighboring Yokohama. The remaining northern portions of the district were annexed in 1911 and 1927. On October 10, 1927 the 14 former towns and villages were re-organized as Isogo Ward within the city of Yokohama.