Mo. Rev. Stat. § 7.001
The boundaries of the state of Missouri have been fixed as follows:
The enabling act of Congress (March 6, 1820), authorizing the admittance of Missouri into the Union, described the boundaries of Missouri as follows: (Section 2, Act of Admission, RSMo 1959, Volume 5)
"Beginning in the middle of the Mississippi River, on the parallel of thirty-six degrees of north latitude; thence west, along that parallel of latitude, to the St. Francis River; thence up and following the course of that river, in the middle of the main channel thereof, to the parallel of latitude thirty-six degrees and thirty minutes; thence west along the same to a point where the said parallel is intersected by a meridian line passing through the middle of the mouth of the Kansas River, where the same empties into the Missouri River; thence from the point aforesaid, north, along the said meridian line, to the intersection of the parallel of latitude which passes through the rapids of the river Des Moines, making the said line to correspond with the Indian boundary line; thence east from the point of intersection last aforesaid, along the said parallel of latitude, to the middle of the channel of the main fork of the said river Des Moines; thence down and along the middle of the main channel of the said river Des Moines, to the mouth of the same, where it empties into the Mississippi River; thence due east to the middle of the main channel of the Mississippi River; thence down and following the course of the Mississippi River, in the middle of the main channel thereof, to the place of beginning."
The present counties of Atchison, Nodaway, Holt, Andrew, Buchanan and Platte, located in the northwestern corner of the state were not then included within the boundaries. These six counties were acquired by what is known as "The Platte Purchase", an act of Congress, approved June 7, 1836 (U.S. Statutes at Large, 34, entitled "An Act to extend the western boundary of the State of Missouri to the Missouri River"). In Cooley v. Golden, 52 Mo.App. 229, it was decided that this carried the western boundary of the state to the center of the channel of the Missouri River and that Missouri and Nebraska have concurrent jurisdiction over the river.
In 1849 a dispute arose between Missouri and Iowa as to the true location of the boundary line dividing the two states. An action was filed in the United States Supreme Court and it was determined that the northern boundary of Missouri was the Osage line as run by Sullivan in 1816, from the northwest corner made by him to the Des Moines River; and that a line extended due west from said northwest corner to the Missouri River was the proper northern boundary of the territory included in the Platte Purchase. (Missouri v. Iowa, 7 How. 660.)
In 1870 an action was filed in the Supreme Court of the United States to establish the boundary between the states of Missouri and Kentucky at a point on the Mississippi River, twenty miles below the mouth of the Ohio, known as Wolf Island. It was determined that the boundary line ran along the center of the main channel of the river, as the river had been in 1820 at the time Missouri was admitted into the Union. It was found that at that time the main channel of the Mississippi had been on the western side of Wolf Island. Thus, Wolf Island was within the Kentucky boundary. (Missouri v. Kentucky, 11 Wall. 395.)
Again in 1937, Missouri commenced suit against Iowa in the Supreme Court of the United States to determine the boundary between Clark County in the state of Missouri and Lee County in the state of Iowa. A stipulation was filed whereby it was proposed that the legislatures of Missouri and Iowa pass like bills, Missouri relinquishing to Iowa all jurisdiction to lands lying north and east of the Des Moines River then in Clark County, Missouri, and Iowa relinquishing to Missouri all lands lying south and west of the Des Moines River, then in Lee County, Iowa. Missouri and Iowa each passed such bill. (Laws of Missouri, 1939, p. 476; Iowa, 48th general assembly, chapter 304.) The acts were submitted to the Congress of the United States and approved August 10, 1939. (Pub. Res. No. 74, 76th Congress.)
A controversy over the boundary between Missouri and Kansas is made the subject of a 1949 act (Laws of Missouri 1949 page 311) wherein it is provided that "the center of the channel of the Missouri River, as its flow extends from its intersection with the fortieth parallel, north latitude, southward to the middle of the mouth of the Kansas or Kaw River" shall be the boundary between such states. The act was not to become operative unless Kansas enacted a similar law relinquishing sovereignty over lands lying on the Missouri side of the center of the channel, within two years from its effective date. The corresponding Kansas law appears in General Statutes of Kansas of 1949, sections 82a-521 to 82a-527.
In 1981, the 1st regular session of the 81st general assembly, by House Bill No. 147, acted to settle a boundary dispute with the state of Kansas concerning certain property in the vicinity of the French Bottoms near St. Joseph, Missouri. The general assembly ratified and affirmed a boundary survey which set the boundary line as the thalweg line (deep water line) of the channel of the Missouri River, abandoned by avulsion in April, 1952. The corresponding Kansas law appears in Kansas Statutes Annotated 1980 Supplement, sections 82a-527a and 82a-527b. Ratified by Congress by H.R. 4048. Signed by the President on October 16, 1981.
§ 7.001, RSMo