This Elijah J. Lee, CO F (Marion's Men) 7th. Regiment, Miss. Infantry, was a resident of Jones County in 1860, his widow, Eliza M. Lee, filed for the pay due him at the time of his death 1 Aug 1862. As you noted, he was killed in a train crash, this occurred in Greenville , AL. He can be found in the 1850 Covington County Federal Census in the household of William Lee.
1860 Federal Census
Name: Elijah Lee
Age in 1860: 24
Birth Year: abt 1836
Birthplace: Mississippi
Home in 1860: Jones County, Mississippi
Gender: Male
Post Office: Ellisville
Household Members:
Name / Age / Born
Elijah Lee 24 MS
Eliza M Lee 22 MS