And having been to many in Mobile, I find it hard to believe that St. Louis has something of greater size.
Soulard is a historic neighborhood in St. Louis, Missouri. It is a thriving, eclectic area; and is home to the second largest Mardi Gras celebration in the United States and a popular Farmers' market.
It's listed in the encyclopedia as the second largest. I didn't make it up. But if you want to think of Mobile or any other city as being "second largest" that's fine with me. Personally, I detest the idea of "mardis gras." :)
St. Louis gets about 1/2 a million people in for the Mardi gras parades and parties. Not as wild as NO, but wild enough that I have never been downtown for one. They have been celebratig it for 25 years or so.
It is the 2nd largest Mardi Gras in the UA. Google it.