United States Statutes at Large/Volume 5/25th Congress/3rd Session/Chapter 91
Chap. XCI.—An Act to define and establish the eastern boundary line of the Territory of Iowa.
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled,Eastern boundary of Iowa. That the middle or centre of the main channel of the river Mississippi shall be deemed, and is hereby declared, to be the eastern boundary line of the Territory of Iowa, so far or to such extent as the said Territory is bounded eastwardly by or upon said river: Provided, however, That the said Territory of Iowa shall have concurrent jurisdiction upon the said Mississippi river with any other conterminous State or Territory so far or to such extent as the said river shall form a common boundary between the aforesaid Territory of Iowa and any other such conterminous State or Territory.
Approved, March 3, 1839.