Hi, and welcome to JA!
I have found a US government site that lists the exact information you are looking for.
In the lists below, the plant name is XXXXX XXXXX the county name in parentheses.
The following plants use coal as their primary source for at least some of their generator units:
The following plants use coal as an alternative (or backup) source:
Here are the relevant pages, listing all of the power plants in Mississippi. There is a key at the bottom to help you identify the symbols for coal (such as "BIT" for bituminous coal), versus other types of power (such as "NG" for natural gas):
I hope this helps,