 In 1824, treaties for the Ioway, Sac and Fox ceding their land in Missouri implied that the Sullivan Line was Missouri's northern border all the way to the Mississippi.Missouri did not formally move to claim the land south of the Sullivan Line to the mouth of the Des Moines at Keokuk, Iowa became known as Half Breed Tract and was declared part of Iowa when it joined the Union in 1846.Since it is south of the Sullivan Line it is the southernmost point in Iowa.