It is named for the Portage between the Fox and Wisconsin Rivers, in Portage proper. Today, Portage is in Columbia County.
The seat and largest city is Stevens Point,
It borders Marathon, Shawano, Waupaca, Waushara, Adams and Wood Counties.
Main highways include I-39, US-51, US-10, WI-34, WI-49, WI-54 and WI-73.