- a state in the southern US, on the Gulf of Mexico; population 4,410,796 (est. 2008); capital, Baton Rouge. Louisiana originally denoted the large region of the Mississippi basin claimed for France by the explorer La Salle in 1682. It was sold by the French to the US in the Louisiana Purchase of 1803. The smaller area now known as Louisiana became the 18th state in 1812.
named in honour of Louis XIV