I've never heard that expression;nor do I know a "Cooter!"

"Drunk as Cooter Brown!" - Folklore has it that Cooter Brown had family on both sides during the Civil War and he didn't want to fight for either side. So he got drunk, stayed drunk throughout the war years, and was not drafted. Now a person's intoxication is measured to his.

I've never heard that...is it a regional expression?

DRUNK AS COOTER BROWN - adj. phrase. Also "drunk as Cooter, ~ Cooty Brown. Chiefly South. Very intoxicated. "This is a Black expression very familiar to the informant, who is from New Jersey. She says it is current and, so far as she knows, it 'came up with the Blacks from the Carolinas.' She thinks it probably derives from some proverbial drunkard." From "Dictionary of American Regional English," Volume 1 by Frederic G. Cassidy (1985, Belknap Press of Harvard University Press, Cambridge, Mass., and London, England). Page 769-770. http://www.phrases.org.uk/bulletin_board/20/messages/532.html

Oh yes. I've heard it many times. Here is what Wikipedia says: "Cooter Brown is a name used in metaphors for drunkenness, mostly in the southern United States. Cooter Brown supposedly lived on the Mason-Dixon, which divided the North and South during the civil war, making him eligible for military draft by either side. He had family on both sides of the Mason-Dixon, so he did not want to fight in the war. He decided to get drunk and stay drunk for the duration of the war so that he would be seen as useless for military purposes and would not be drafted. Inebriety has been measured against Cooter Brown's extended binge ever since by use of the metaphors "as drunk as Cooter Brown" or "drunker than Cooter Brown." It has not been determined whether or not Cooter Brown is a factual person, or a part of American folklore." http://tinyurl.com/ys2vjk

Cooter Brown was a half-breed (Half Cherokee, Half Black) who lived in south Louisiana on a small plot of land given to him by an old Cajun fur trapper. Cooter lived alone in the old Cajun's shack. When the civil war broke out, Cooter didn't want to choose sides, because he didn't know who might win. He didn't like people much and was fearful of either side. Because of this, Cooter, who was a heavy drinker anyway, began drinking all the time. Cooter always dressed like an indian so as to confirm the fact that he was an indian and not a negro. And as such, he was a free man. Whenever soldiers (Yanks or Rebels)showed-up in the area they would always find him drunk. Often times he'd offer the soldiers a drink. Word began to spread about the crazy, drunken indian named Cooter Brown. By the time the war ended, Cooter couldn't stop drinking if he had wanted to. One night his shack caught fire and burned completely to the ground. When locals investigated the burned site the next day there was nothing that remained of Cooter's body. They surmised that old Cooter had so much alcohol in him that he had just burned up. Since then Cooter Brown has been synonymous with inebriety. Submitted by: Willie the Wet Weasel