St. Clair County is a county located in the U.S. state of Michigan and bordering the west bank of the St. Clair River. As of the 2010 census, the population was 163,040. 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.
Defined Inspections provides radon testing in St. Clair County for $100 per 48-hour continuous monitoring test.