Originally called St. Clairsville and platted in 1801, Decatur was named for early 19th century naval hero Stephen Decatur. It is among the oldest villages in Brown County, which before 1817 was part of Adams County. Notable early residents included Nathaniel Beasley, the first surveyor of Adams County, and Sarah Boone Montgomery, a heroine of the border wars in Kentucky. Decatur and Byrd Township supported at least four known stations on the Underground Railroad, and many area residents helped conduct escaping slaves northward to freedom. Albert Nelson Marquis, born in Decatur and reared in nearby Hamersville, began his own publishing company in Cincinnati at age 21, moved A.N. Marquis and Co. to Chicago in 1884, specialized in business directories, and published the first edition of Who's Who in America in 1899. The immediately successful "Big Red Book" listed biographical information about nationally significant individuals, inspired many similar topical references, and remained under Marquis's leadership as editor in chief until 1940, while Who's Who in America continued as a standard reference on accomplished living Americans.