A Yellow Fever epidemic wiped out the old town of Cincinnati in 1853. The town was a shipping point on the Trinity River which is between Walker County and Trinity County. The story is that a sailor or passenger who came up the river by boat carried the disease, People were stricken so fast that there were hardly enough to bury the dead. People fled the area and this spread the fever to other areas. This may be too early to account for deaths in your family.
Another peson that responded to this query mentions the general lawlessness in Trinity Co. after the Civil war and that may be a factor also.