Oregon Territory is organized by act of Congress.
An Act of Congress is a statute enacted by the United States Congress. Acts may apply only to individual entities (called private laws), or to the general public (public laws). For a bill to become an act, the text must pass through both houses with a majority, then be either signed into law by the president of the United States or receive congressional override against a presidential veto.
The Territory of Oregon was an organized incorporated territory of the United States that existed from August 14, 1848, until February 14, 1859, when the southwestern portion of the territory was admitted to the Union as the State of Oregon. Originally claimed by several countries (see Oregon Country), the region was divided between the UK and the US in 1846. When established, the territory encompassed an area that included the current states of Oregon, Washington, and Idaho, as well as parts of Wyoming and Montana. The capital of the territory was first Oregon City, then Salem, followed briefly by Corvallis, then back to Salem, which became the state capital upon Oregon's admission to the Union.