An act of the State Legislature on March 1, 1851, authorized the incorporation of the City of Carondelet. It was divided into three wards and authorized election of a mayor and two councilmen from each ward. In 1862, the city offices were moved to Lafayette Hall at the southeast corner of Broadway and Loughborough. This landmark, later converted to commercial uses, was destroyed by fire in 1949. During the late 1860's, the city began to attract many industries and prospered after opening of the Iron Mountain Railroad from St. Louis.
The political complexion of Carondelet changed during the Civil War. Older inhabitants were generally Democrats, whereas the more recently arrived Germans were Republican and Northern sympathizers. At the 1859 city election only two Democrats were elected, all other offices going to the Republicans, who dominated the city's life for many years. Henry T. Blow remained the leader of the pro-Union people during the war years. Southern sympathizers rallied to join the Confederate Army under Captain John S. Bowen, who, as a general, died of complications from the effects of the siege of Vicksburg.
A special census in 1865 reported the population of Carondelet to be 4,534. Native Americans comprised 3/8 of the total, while Irish and Germans comprised 1/4 each and French and Creoles were the remaining 1/8. On the first Tuesday in April, 1870, by act of the legislature, Carondelet was annexed to the City of St. Louis, amid much bitterness among Carondelet residents who had no voice in the precedings.
Until 1900, Carondelet continued to be a pleasant place to live, having enjoyed the extension of city services after the 1870 merger with St. Louis. With the advent of the twentieth century, a gradual decline began in the area to the extent that considerable rehabilitation is now necessary, especially in the older portions of Carondelet.