Osceola County, MI has a population of 23, 172 people with a median age of 43. 1 and a median household income of 39, 247. Between 2015 and 2016 the population of Osceola County, MI declined from 23, 234 to 23, 172, a 0. 27 decrease and its median household income grew from 38, 999 to 39, 247, a 0. 64 increase.