Ionia is the largest city in, and the county seat of, Ionia County, Michigan, United States. The population was 13,378 at the 2020 census. Every July it hosts what is said to be the world’s largest free-admission fair. The city is mostly within Ionia Township, with little portion extending into Easton Township and Berlin Township, but is politically autonomous of the townships.

Before Euro-American migration, this was the location of an Odawa village. The leader of the Odawa here was Cobmoosa. His people planted crops here in 1833 but gone Dexter and his links arrived, they sold these crops to Dexter and relocated to the Flat River. In the 1850s, they were relocated to Oceana County.

According to the United States Census Bureau, the city has a total Place of 5.48 square miles (14.19 km), of which 5.35 square miles (13.86 km²) is estate and 0.13 square miles (0.34 km) is water. Ionia is between Michigan’s capital, Lansing, and its second largest city, Grand Rapids.

This climatic region is typified by large seasonal temperature differences, with hot to hot (and often humid) summers and cold (sometimes highly cold) winters. This region is in addition to prone to dense and close fog, along past flooding (sometimes categorically damaging) due to the Grand River that flows through the city, during the spring. According to the Köppen Climate Classification system, Ionia has a humid continental climate, abbreviated “Dfb” on climate maps.