Keweenaw County is the northernmost county in Michigan. According to the U.S. Census Bureau, the county has a total area of 5,966 square miles (15,451.9 km2), of which 541 square miles (1,401.2 km2) is land and 5,425 square miles (14,050.7 km2) (90.932%) is water. Of all counties (or county-equivalents) in the United States, Keweenaw County has the highest proportion of water area to total area.
In essence, 90.932 percent of the county consists of a significant part of Lake Superior, while only 9.068 percent is actually land. Isle Royale is its northernmost section. It is the largest county in the largest state east of the Mississippi River.