Michigan Counties
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Michigan Counties

The boundaries of the eighty-three counties in Michigan have not changed substantially since 1897. Wayne County was the sixth county in the Northwest Territory, formed 15 August 1796 and organized in 1815. Wayne County was created 21 November 1815 as an original county of Michigan.

St. Clair County, Michigan

St. Clair County Education, Geography, and HistorySt. Clair County, Michigan Courthouse

St. Clair County is a county located in the state of Michigan bordering the St. Clair River. Based on the 2010 census, the population was 163,040. It is the 13th-most populous county in the state, and 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. St. Clair County is either named for Arthur St. Clair, first governor of the Northwest Territory, or for Saint Clair on whose feast day Lake St. Clair was discovered.

St. Clair County is part of the Detroit-Warren-Dearborn, MI Metropolitan Statistical Area. Geographically, it lies in the Thumb area of eastern Michigan.

Etymology - Origin of St. Clair County Name

An expedition led by the French explorer René Robert Cavelier, Sieur de La Salle named the namesake lake as Lac Sainte-Claire, because they entered the lake on August 12, 1679, the feast day of Sainte Clare of Assisi. The lake is named on English maps as early as 1710 as Saint Clare. 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 Saint Clair and the St. Clair River, the county was named for them.

The name is sometimes attributed to honoring the American Revolutionary War General and Governor of the Northwest Territory Arthur St. Clair, but it was established with the current spelling long before St. Clair was a notable figure. The earlier spelling of the lake's name may have been conflated with that 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 attributed to honoring Patrick Sinclair, a British officer who purchased land on the St. Clair River at the outlet of the Pine River. In 1764, he built Fort Sinclair there, which was in use for nearly 20 years before being abandoned.


County QuickFacts: CensusBureau Quick Facts

St. Clair County History

St. Clair County is either named for Arthur St. Clair, first governor of the Northwest Territory, or for Saint Clair on whose feast day Lake St. Clair was discovered.

Set Off: 1820

Organized: 1821

Geography: Land and Water

As reported by the Census Bureau, the county has a total area of 837 square miles (2,170 km2), of which 721 square miles (1,870 km2) is land and 115 square miles (300 km2) (14%) is water. St. Clair County is one of five counties that form the peninsula, known as the Thumb, that projects into Lake Huron. St. Clair County is closely connected in terms of economy with its neighbors, Metropolitan Detroit and Sanilac County in Michigan, and Lambton County in Ontario, Canada. Saint Clair County is the principal county in the The Blue Water Area, a subregion of the Thumb.

Neighboring Counties

Bordering counties are as follows:

  • Sanilac County (north)
  • Lapeer County (west)
  • Macomb County (south)
  • Lambton County, Ontario (east)
  • Across Lake St. Clair lies Chatham-Kent, Ontario (southeast)


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