Hawaii County is a county in the U.S. state of Hawaii in the Hawaiian Islands. It is coextensive with the Island of Hawaii, often called the "Big Island" to distinguish it from the state as a whole. The 2020 Census population was 200,629. The county seat is Hilo. There are no incorporated cities in Hawaii County. The Hilo Micropolitan Statistical Area includes all of Hawaii County. Hawaii County has a mayor–council form of government. In terms of geography, Hawaii County is the most expansive county in the state and the most southerly county in the United States.

Hawaii is the largest island in the United States, located in the eponymous state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of 4,028 square miles (10,430 km2), it has 63% of the Hawaiian archipelago's combined landmass. However, it has only 13% of the archipelago's population. The island of Hawaiʻi is the third largest island in Polynesia, behind the north and south islands of New Zealand.