The St Louis Cemetery is now a three part Roman Catholic Cemetery in New Orleans. It is probable that Louis is referring to what is now St Louis Cemetery #1, which opened in 1789 and became the main burial ground in New Orleans. The image here shows Cemetery #1.
St Louis Cemetery #2 opened in 1823, and #3 in 1854. As with the Lafayette Cemetery, the bulk of the graves are above ground tombs or vaults.