When one speaks of the Missississi Delta, he might be speaking of the region in NW Mississippi, SE Arkansas, or NE Louisiana. It is the fertile area created by years of flooding by the Mississippi River.
Technically it is an alluvial plane as opposed to a delta--see geology 101 for the difference.
In any even event when one is in the State of Mississippi he is speaking of an area centered roughly east of a line from Memphis to Vicksburg.
My son lives in a small community north of Bastrop Louisiana; so small that he lives in the woods, where everybody should live--the woods--or at least somewhere where birds, frogs, crickets, etc. can be heard. He was reared in Houston, Texas, so his recent move has taken him from hell to heaven. When I visit him in the "delta" it is, regarding the people, the land, the traditions like going home. I love Texas, but Houston, like all of the "New South" cities has taken on a non-southern flavor.
I would recommend to anyone and everyone, James Everett Kibler's WALKING TOWARD HOME for a taste of what I mean.