This cache is not at the posted coordinates, and neither location is the St. Joseph River.
The St. Joseph River (known locally as the St. Joe) is a tributary of Lake Michigan with a length of 206 miles. The river flows in a generally westerly direction through southern Michigan and northern Indiana, to its terminus on the southeast shore of the lake. The St. Joseph River main stem is 206 miles long, rising in southern Michigan in Hillsdale County, flowing from Baw Beese Lake, within 5 miles of the headwaters of the OTHER St. Joseph River of the eastward-flowing Maumee River watershed.
Baw Beese Lake was historically named for the Potawatomi Chief Baw Beese.
Saakiiweesiipiiwi (Outlet River, also historically spelled Sakiwasipi), as it was called by the Miami people, was inhabited for thousands of years by various indigenous tribes as it served an essential trade avenue in the Great Lakes region. Cache location: N 42° 5.318' W 85° 23.486'
The cache hide is pretty much exactly what you'd expect for the location you will arrive at.