St. Clair County located in Michigan's lower peninsula and bordering the west bank of the St. Clair River. As of the 2020 census, the population was 160,383. It is the 13th-most populous county in the state. The county seat is Port Huron, located at the north end of the St. Clair River at Lake Huron. The county was created September 10, 1820, and its government was organized in 1821. It is also consider by the State of Michigan to be a part of The Thumb, a peninsula that surrounded by Lake Huron in the east-central area of the state. This area is sometimes dubbed the Blue Water Area.
French explorer René-Robert Cavelier, Sieur de La Salle led an expedition to this area on August 12, 1679. They named the lake as Lac Sainte-Claire, because it was the feast day of Saint Clare of Assisi, whom they venerated. English mapmakers adopted the French name, identifying the lake feature as Saint Clare on maps dated as early as 1710. By the Mitchell Map of 1755, the spelling was given as St. Clair, which is the current version. Located along the western shores of Lake St. Clair and the St. Clair River, the county was named for them by European-American settlers.
The name is sometimes mistakenly attributed to honoring Arthur St. Clair, an American Revolutionary War general and governor of the Northwest Territory, but it was established long before he was considered a notable figure. The earlier spelling of the lake's name may have been conflated with English practice and the name of the general, as several political jurisdictions near the lake and the river, such as St. Clair County, St. Clair Township, and the cities of St. Clair and St. Clair Shores, share this spelling.
The name has sometimes been mistakenly attributed to honoring Patrick Sinclair, a British officer who purchased land on the St. Clair River at the mouth of the Pine River. In 1764, he built Fort Sinclair there, which was in use for nearly 20 years before being abandoned.
St. Clair County is home to:
- Algonac State Park
- Lakeport State Park
- Lake St. Clair Old South Channel Light