From the person who requested some help on Bill Gay Island in Keiths blog. Bill Gay Island is actually located in Red River Parish, and is on the tax assessors roll in Red River Parish.
It is owned by the Bethards, since the 1980's. I quickly looked at the records in Desoto Parish and could not find Roxie Gay's name in 1912.
Its possible that a very small part of it is in Desoto, but Red River Parish claims it.
Have enclosed a aerial map of it, and hope it helps you. Take care now.