Census Information
Per 2020 Census data, the City of Northville's population increased from 5,970 in 2010 to 6,119 in 2020.   Of the 6,119 population in Northville, 3,326 of the population is in Oakland County, and 2,793 of the population is in Wayne County. 

Links for Detailed US Census Information and Population Estimates

US Census Bureau
Explore Census Data (tables, maps, and more)
SEMCOG (community profiles, etc.)