Suzanne, I will do my best to help you.

First off we know from the 1930 census that Louis reported that his father was German and his mother from Mississippi. How would he have known this? He would have been 10 or 11 years old in 1909, assumming he was born in 1898 as his age was 31 in the census. A 10 year old would have remembered this? Lets say yes he would.
So now we need to find a Kathman in Mississippi where his mother was born. It may not work but it is worth a try.
There are three seperate Kathman(n) lines that are all from Oldenburg Germany, so we might be lucky and find the correct connection.
I may have to have more information on birth dates of Maria Katherine and Louis (William?) which means we will have to send e-mail off list to keep personal data private.

Darrell