Louisiana is 15.9% French (or French Canadian) ancestry, 4.8% Italian ancestry.
Mississippi is 2.7% French ancestry, 1.9% Italian ancestry.
Orleans Parish, LA is 6.8% French ancestry, 4.2% Italian ancestry.
Jefferson Parish, LA is 18.4% French ancestry, 10.8% Italian ancestry.
This is of course declared ancestry. Many of those putting down their ethnicity as American in NOLA are quite likely to be of French heritage. Especially in Jefferson.
I've always wished the census would get rid of the American ethnicity.
I'd rather go the other way and remove ethnicity except where required for the VRA. At one time the Census only asked for the place of birth and that seems fine. In our melting pot society after three generations there are relatively few people who are of only one country of origin and it doesn't tell us much in Census statistics.
The ACS asks about ancestry, not the census. Why intentionally cripple such an deep and interesting source of data?
Because as Al points out it is inconsistent and often misleading for that reason. To me the ACS is part of the Census. The ACS replaced the long form of the decennial Census with rolling annual and multiyear averages, but it is still the same organization and data type.
I like the current proposals to roll race, ethnicity, and ancestry into a single question. It is more neutral as to what the data will be used for. Thus Irish, Swedish, and Italian would be subcategories of White, just as Puerto Rican, Mexican, and Salvadoran are subcategories of Hispanic, and Haitian and Afro-American could be subcategories of Black.
