Yezo, Or Yesso, formerly the name of the uncivilized part of Japan above lat. 38° N., now of one of the four large islands of Japan, between lat. 41° 24' and 45° 31' N., and Ion. 139° 40' and 146° 7' E., separated from Saghalien or Karafto on the north by La Perouse strait, and on the south from the main island of Japan by the narrow strait of Tsugaru; extreme length, 290 m.; breadth, 245 m.; estimated area, about 30,000 sq. m.; pop. about 125,000. The coast is bold and rocky, but indented with several good harbors. The surface generally is mountainous, with many volcanoes, solfataras, and hot springs. There are some small lakes and numerous mountain torrents. The principal river is the Ishikari, rising near the middle of the N. part of the island and flowing S. W. about 165 m. to Strogonoff bay. Bears, wolves, deer, and all kinds of sea fowl abound. The principal producions are coal, petroleum, salt, sulphur, timber (of which 33 valuable kinds are found), deer skins, dried fish, and fish oil. The population, including some Chinese, Europeans, and Americans, is settled chiefly in the south. The north is thinly inhabited by Ainos, who number about 20,000, living in a few fishing villages.

The interior was entirely unsettled and unexplored till the present government took steps for colonizing the island, employing Americans, who have explored a great part of the country, built roads, laid out farms, and introduced stock and seeds from the United States. The chief towns are Hakodate (Hakodadi), Matsumae, Esashi, and Sapporo. (See Japan).