Detroit was incorporated as a town by the legislature of the Northwest Territory at Chillicothe, Ohio, and approved by Territorial Governor Arthur St. Clair on January 18, 1802, effective February 1, 1802. Government was administered by a five-person board of trustees and there was no office of mayor.
Shortly thereafter, on February 23rd, the board of trustees for the newly created city of Detroit adopts a fire code that requires all residents and business owners to sweep their chimneys often. It also provides buckets and ladders to residents, who are required to turn out to fight any fires.
Apparently the fear of fire was genuine. On June 11, 1805, Detroit was destroyed by fire when baker John Harvey allegedly sets his barn ablaze with ashes from his pipe.
At the time of its incorporation as a city Detroit was about a third of a square mile, or 213 acres.
History of Detroit Wikipedia Entry.