About two-thirds of all Michigan counties saw their populations of young adults grow between 2020 and 2025, according to new U.S. Census Bureau estimates. Statewide, the number of residents ages 25 to 34 increased by about 0.43%, rising from roughly 1.30 million in 2020 to 1.31 million in 2025. Some counties fared far better, and others far worse, at keeping, growing and attracting these residents.