Portage is a city in Kalamazoo County in the U.S. state of Michigan. The population was 46,292 in the 2010 census. It is the smaller of the two main cities included in the Kalamazoo-Portage Metropolitan Statistical Area, which has a population of 326,589 as of 2010.Portage is adjacent to the southern boundary of the City of Kalamazoo.