Marquette is the county seat of Marquette County and the largest city in the Upper Peninsula of Michigan, United States. Located on the shore…Marquette is the county seat of Marquette County and the largest city in the Upper Peninsula of Michigan, United States. Located on the shores of Lake Superior, Marquette is a major port known primarily for shipping iron ore from the Marquette Iron Range. The city is partially surrounded by Marquette Township, but the two are administered autonomously.