Ionia is the largest city in, and the county seat of, Ionia County, Michigan, United States. The population was 10,569 at the 2000 census. Every late July (ending on the last Saturday of July and beginning 10 days previous) it hosts what may be the world's largest free-admission fair. The city is mostly within Ionia Township, with small portion extending into Easton Township and Berlin Township, but is politically autonomous of the townships.
According to the United States Census Bureau, the city has a total area of 5.2 square miles (13.5 km²), of which, 5.0 square miles (13.1 km²) of it is land and 0.2 square miles (0.4 km²) of it (3.07%) is water. Ionia is between Michigan's state capital, Lansing, and its second largest city, Grand Rapids.
As of the census of 2000, there were 10,569 people, 2,421 households, and 1,534 families residing in the city. The population density was 2,095.9 per square mile (809.7/km²). There were 2,621 housing units at an average density of 519.8 per square mile (200.8/km²). The racial makeup of the city was 71.08% White, 21.94% African American, 1.05% Native American, 0.65% Asian, 2.13% from other races, and 3.15% from two or more races. Hispanic or Latino of any race were 5.08% of the population.