The Montana Territory had been organized out …

Years: 1864 - 1864
May

The Montana Territory had been organized out of the existing Idaho Territory by Act of Congress and signed into law by President Abraham Lincoln on May 26, 1864.

The areas east of the Continental Divide had been previously part of the Nebraska Territory and Dakota Territory and had been acquired by the United States in the Louisiana Purchase.

The territory also includes a portion of the Idaho Territory west of the continental divide and east of the Bitterroot Range, which had been acquired by the United States in the Oregon Treaty, and originally included in the Oregon Territory.

The part of the Oregon Territory that becomes part of Montana had been split off as part of the Washington Territory.

The Territory of Montana, an organized incorporated territory of the United States, comes into existence on May 28, 1864.

The boundary between the Washington Territory and Dakota Territory had been the Continental Divide; however, the boundary between the Idaho Territory and the Montana Territory follows the Bitterroot Range north of 46°30'N (as shown on the 1864 map).

Popular legend says a drunken survey party followed the wrong mountain ridge and mistakenly moved the boundary west into the Bitterroot Range., but, contrary to legend, the boundary is precisely where the United States Congress intended.

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