The Louisiana Death Index is online (FREE).
All State death records before 1957 can be obtained from the Louisiana State Archives in Baton Rouge (off Essen Lane).
There is an online order form OR you can call them for additional information, if needed.

If you are close enough to go in person, it will cost you $.50 per page, self-serve. You can browse the certificates on microfilm before purchasing.

A local Genealogical Society would also be a great help.
Most will allow FREE queries in their member publication.
Many have Genealogy Seminars. Here you can learn basic research techniques. Through networking, you can meet genealogists from the area, who may know MUCH more about Plaquemines parish, its history, and its people.

http://www.lacreole.org [only ONE of the specialized Gen. Societies]
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LSA Death Index: Click on 'Advanced Search', fill in the surname and (opt.) First name. You can also select a parish to narrow the search.