In the Edo Period, it was part of Morioka Domain and prospered through trade with the Kansai region, exporting particularly hinoki cypress and sea cucumber in exchange for cloth.

Yokohama was also a post town on the Tanabe kaidō, a highway to the north shore of the Shimokita Peninsula from where travelers could take a boat to Ezo (Hokkaido).

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

Yokohama is part of Shimokita District which, together with the city of Mutsu, contributes three members to the Aomori Prefectural Assembly.

In terms of national politics, the town is part of Aomori 2nd district of the lower house of the Diet of Japan.