Decatur is the largest city and the county seat of Macon County in the U.S. state of Illinois, with a population of 76,122 as of the 2010 Census. The city was founded in 1829 and is situated along the Sangamon River and Lake Decatur in Central Illinois. Decatur's estimated population for 2019 was 70,746. Decatur is the seventeenth-most populous city in Illinois Decatur is listed by the United States Census Bureau as number 3 in "The 15 Fastest-Declining... Show more

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