There are 88 counties in Ohio. In 2019, Ohio's Franklin County, home of Columbus, has the highest population in the state with 1,310,300 residents. This represents growth of 12.35% since the last census. The next-largest counties are Cuyahoga County (1,243,857) with the city of Cleveland, Hamilton County (816,684) with the city of Cincinnati, Summit County (541,918), and Montgomery County (532,331). These are the only counties in Ohio exceeding 500,000 residents. Of these counties, Franklin County experienced the most rapid growth while Cuyahoga County experienced growth of -2.68%.
There are no counties in Ohio with fewer than 10,000 residents. The least populated county in Ohio is Vinton County with 13,139, a decline of 1.98%. Other small counties in Ohio include Monroe County (13,790), Noble County (14,354), Morgan County (14,604), Harrison County (15,174), and Paulding County (18,760). All of these counties have experienced a decline in population. Monroe County had the largest decline of 5.60%. Of Ohio's 39 counties with a population below 50,000, all but five experienced a decline in population ranging from -0.02% to -6.12% in the case of Carroll County.
Delaware County, Ohio experienced the most rapid growth in the state since the last census, climbing 16.98% to 204,826 residents in 2019. Other cities with major growth include Franklin County (12.35%), Union County (10.35%), Warren County (8.77%), and Fairfield County (6.41%). The county with the most rapid decline is Carroll County at -6.12% population growth followed by Jefferson County (-5.60%), Monroe County (-5.60%), and Trumbull County (-5.34%).