Michigan Territory separated from Indiana Territory
The Territory of Michigan was an organized incorporated territory of the United States that existed from June 30, 1805, until January 26, 1837, when the final extent of the territory was admitted to the Union as the State of Michigan. Detroit was the territorial capital.Beginnings of American rule
By proclamation of acting governor and territorial secretary Winthrop Sargent, the "first" Wayne County was established from Knox and Hamilton counties on August 15, 1796, and included most of the area that later became the Michigan Territory, as well as portions of what are now Ohio and Indiana.
In 1800, the western half of the Lower Peninsula and most of the Upper Peninsula were attached to the Indiana Territory when it was established as a separate government from the Northwest Territory. Wayne County was thereby reduced to the remainder of the two peninsulas, and continued under the government of the Northwest Territory. St. Clair County, another Indiana Territory county, was also expanded at this time to include the western portion of the Upper Peninsula and a small sliver of the Lower Peninsula along the shore of Lake Michigan.
When Ohio was admitted as a state in early 1803, the eastern half of Michigan was incorporated into the Indiana Territory. One of the first acts taken that year by the Indiana government under William Henry Harrison was to reorganize Wayne County under Indiana law, adding territory from Knox and St. Clair counties. Michigan's first county now encompassed all of the Lower Peninsula, much of the Upper Peninsula, and those portions of today's Illinois, Indiana, and Wisconsin that drained into Lake Michigan.  In many respects, the change from the government of the Northwest Territory to that of the Indiana Territory had little effect on Wayne County's limited operations. By Governor Harrison's proclamation of January 11, 1803, the courts of Wayne County—common pleas, orphans, and quarter sessions—kept their organization under the new territorial government, with almost identical composition.
But the logistics of government went from difficult to almost impossible, with the mail between Detroit and the capital at Vincennes being routed at one point through Warren in northeastern Ohio. The deciding factor may have come when an election was called by Governor Harrison for September 11, 1804, to decide whether Indiana Territory (which by this time was responsible for not only the settlements in Michigan, Wisconsin and Illinois, but the newly acquired District of Louisiana as well) should progress to the second stage of territorial government. But word failed to reach Detroit until after the date had passed, and the settlers of Michigan petitioned Congress in December 1804, asking that Wayne County be set off as an independent territory.