Portage is a city in Kalamazoo County, Michigan, United States. The population was 48,891 at the 2020 census. It is the smaller of the tw…Portage is a city in Kalamazoo County, Michigan, United States. The population was 48,891 at the 2020 census. It is the smaller of the two main cities included in the Kalamazoo-Portage Metropolitan Statistical Area, which had a population of 261,670 in 2020.