The Portage River is located in northwestern Ohio with its mouth at Port Clinton
in Ottawa County
Four main branches or forks are the main tributaries of the river and include the North Branch, which rises in southwest Wood County and flows northeast past Bowling Green; the Middle Branch, which rises in western Hancock County and nearly parallels the North Branch; the South Branch, which rises in northeastern Hancock county and flows north and the East Branch, which rises in eastern Hancock county flowing north through Fostoria.
The South Branch empties into the East Branch about 10 miles northwest of Fostoria while the Middle joins the East about 5 miles east of Bowling Green and continues on meeting the North in Pemberville to form the Portage. From there the river flows east-northeasterly about 30 miles before emptying into Lake Erie at Port Clinton.