Originally Indiana Territory extended westward to the Mississippi and northward to the Canadian boundary. IN 1805 a division was mad by a line running eastward from the southern extremity of Lake Michigan and north of this line the Territory of Michigan was created. Again, by a congressional act of February 3, 1809, all that country lying west of the Wabash River and of a line drawn due north from Vincennes to the Canadian line was constituted as separate territory and called Illinois. This gave to Indiana its present limits except that subsequently the Michigan line was shifted ten miles north of the southern extremity of the lake.

The eastern part of the Michigan peninsula was not at first a part of Indiana Territory, as the line separating the latter form what is now Ohio extended north to Canada till the formation of the State of Ohio in 1802, when the country cut off by Ohio's northern boundary was added to Indiana. The western boundary of Ohio as established at that time shifted the line that had previously formed the eastern boundary of Indiana, thus forming the "Gore."