Izumi-ku (泉区) is one of the 18 wards of the city of Yokohama in Kanagawa Prefecture, Japan. In 2010 the ward had an estimated population of 155,674 and a density of 6,620 persons per km². The total area was 23.51 km². Izumi Ward is located in eastern Kanagawa Prefecture, and on the central-western borders of the city of Yokohama. The area is largely flatland, with scattered small hills.
The area around present-day Izumi Ward has been inhabited continuously for thousands of years. Archaeologists have found stone tools from the Japanese Paleolithic period and ceramic shards from the Jomon period, and tombs from the Kofun period at numerous locations in the area. Under the Nara period Ritsuryō system, it became part of Kamakura and Kōza Districts in Sagami Province.
In the Heian period, it was divided between shōen controlled by the Ōba clan and the Kamakura clan (of which Kamakura Gongorō Kagemasa was the most illustrious member). By the Kamakura period, much of the area was farmland supporting the population of nearby Kamakura. During the Edo period, the territory came under the control of Tokugawa Ieyasu. It was administered as tenryō territory controlled directly by the Tokugawa shogunate, but administered through various hatamoto.