But it turns out that Katrina may not be to blame after all.
Greg Rigamer, a demographer and president of GCR & Associates, a New Orleans consulting firm, said the state's growth was so sluggish in the past decade that it was on track to lose a seat in the House of Representatives and one of its nine electoral votes anyway.
Between 2000 and 2005, the nation's population grew at a rate of 5 percent. In the South, the fastest-growing region, the population grew at 7.5 percent, Rigamer said. Louisiana's population growth rate, by comparison, was less than 1 percent for the first five years of the decade, and 1.4 percent for the whole decade, the lowest among Southern states.
"So it's not Katrina," he said. "Louisiana just wasn't on pace with the rest of the country. It kind of got lost in the spread."
Louisiana is one of eight states to lose one congressional seat. New York and Ohio lost two. Neighboring Texas gained four. Louisiana now ranks as the 25th largest state; in 2000, it ranked as 22nd. The state's population is 4,533,372, an increase from the 2000 population of 4,468,976.
In fact, the population numbers ticked up after Katrina, when billions of dollars in federal money flowed into the state.
U.S. Census Director Robert Groves declined to speculate Tuesday on Katrina's role in Louisiana's slow growth.
Still, the damage wreaked by Katrina should not be discounted.
Katrina -- and Hurricane Rita, which hit western Louisiana two weeks later -- created one of the largest diasporas in the country's history, as newly homeless hurricane victims spread out across the country in search of temporary housing and work.
"So much of the metro area of New Orleans located to Houston and Dallas," said Allison Plyer of the Greater New Orleans Community Data Center. "What's less understood is that many of the evacuees were displaced within the state."
The city of New Orleans lost more than half of its population after the storm. By July 2006, 11 months later, the city counted just 208,548 residents, down from the 455,188 who lived there in July 2005. The numbers have grown steadily as displaced residents rebuilt and returned home. By last July, New Orleans' population had recovered to 354,850 residents.
"We've drawn young professionals who are spurred on by a sense of American urban adventure, coming to help the city recover," said Clancy DuBos, owner and political columnist for the Gambit Weekly in New Orleans.
New population figures for cities have not yet been released.
New Orleans has attracted new residents. But Plyer said the growth rate has slowed in recent years as the city reached a crucial turning point in its recovery.
"Some folks finally got rebuilt in New Orleans but can't find a job in New Orleans now and they're not coming back until they do. We all understand that," she said.
Growth is tied to a complicated set of factors, including the national recession and thorny urban issues, such as the high concentration of blighted houses throughout the city. New Orleans has a higher percentage of blighted homes, a new report says, than any other city in the country at 25 percent, compared with 24 percent in Flint, Mich.; 23 percent in Detroit; and 20 percent in Cleveland.
The changed demographics in New Orleans will have a greater impact at the state level. The city stands to lose four seats in the Legislature -- three in the House and one in the Senate.
But the loss of clout in Washington can't help in a state that depends heavily on federal funds. More than $100 billion in Katrina aid arrived from Washington.
"It makes a big difference," DuBos said. "We lost a seat in the 1990 census and now we're losing another one. We used to have eight and now we're down to six."