Baton Rouge was incorporated in 1817. In 1822, the Pentagon Barracks complex of buildings was completed. The site has been used by the Spanish, French, British, Confederate States Army, and United States Army and was part of the short-lived Republic of West Florida. In 1951, ownership of the barracks was transferred to the State of Louisiana, and in 1976 it was placed on the National Register of Historic Places.
In 1846, the state legislature designated Baton Rouge Louisiana's new capital to replace "sinful" New Orleans. The architect James Dakin was hired to design the Capitol building in Baton Rouge, with construction beginning in late 1847. Rather than mimic the federal Capitol in Washington, as many other states had done, he designed a capitol in Neo-Gothic, complete with turrets and crenellations, and stained glass, which overlooks the Mississippi. It has been described as the "most distinguished example of Gothic Revival" architecture in the state and has been designated as a National Historic Landmark.
By the outbreak of the Civil War, the population of Baton Rouge was nearly 5,500. The war nearly halted economic progress, except for businesses associated with supplying the Union Army occupation of the city beginning in the spring of 1862. The Confederates at first consolidated their forces elsewhere, during which time the state government was moved to Opelousas and later Shreveport. In the summer of 1862, about 2,600 Confederate troops under generals John C. Breckinridge (the former Vice President of the United States) and Daniel Ruggles tried in vain to recapture Baton Rouge.
After the war, New Orleans served as the seat of the Reconstruction Era state government. When the Bourbon Democrats regained power in 1882, they returned the state government to Baton Rouge, where it has since remained. In his 1893 guidebook, Karl Baedeker described Baton Rouge as "the Capital of Louisiana, a quaint old place with 10,378 inhabitants, on a bluff above the Mississippi".
In the 1950s and 1960s, Baton Rouge experienced a boom in the petrochemical industry, causing the city to expand away from the original center.
A building boom that began in the 1990s continued into the 2000s, during which Baton Rouge was one of the fastest-growing cities in the South in terms of technology, and Metropolitan Baton Rouge was one of the fastest growing metropolitan areas in the U.S. (under 1 million), with 602,894 in 2000 and 802,484 people as of the 2010 census.[ Baton Rouge's population temporarily surged after Hurricane Katrina (2005), as it accepted as many as 200,000 displaced residents.