Details here.
In a nutshell:
New Orleans (Orleans Parish) had 485,000 people in 2000; it's got 188,000 people now. St. Bernard Parish, down from 67,000 to 25,000.
Jefferson and Plaquemines parishes did somewhat better: Jefferson's down from 456,000 to 436,000; Plaquemines is down from 27,000 to 20,000. Jefferson Parish is immediately south of New Orleans, across the Mississippi; Gretna, where the sheriff and his gun-wielding troops blocked the New Orleans refugees from crossing the bridge to safety, is in Jefferson. Plaquemines Parish is the toe of the Louisiana boot.