Delta County is a county in the Upper peninsula in the U.S. state of Michigan. As of the 2010 census, the population was 37,069.
Delta County was surveyed in April, 1843. At that time it included the present territory and all of what is now known as Menominee County, and parts of Dickinson, Iron and Marquette Counties. The name came from its triangular shape, like that of the Greek letter Delta. Delta County was formally organized in 1861.
Escanaba was incorporated as a village in 1866, and in 1867 a lighthouse was established on Sand Point. Also in 1867, a charcoal iron furnace was built in Fayette by the Jackson Iron Company.