Idaho /en-us-Idaho. oggˈaɪdəhoʊ/ is a state in the United States of America. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890 as the 43rd state. Idaho is a mostly mountainous state, with an area larger than all of New England. It is landlocked, surrounded by the states of Washington, Oregon, Nevada, Utah, Wyoming, Montana and the Canadian Province of British Columbia.