Green’s Dictionary of Slang

extremely, very.

1871		E. Eggleston Hoosier School-Master (1892) 72: She was so dog-on stuck up that she turned up her nose one night at a apple-peelin’ bekase I tuck a sheet off the bed to splice out the table-cloth.
1884		C.F. Lummis letter 25 Dec. in Byrkit Letters from the Southwest (1989) 196: I know it’s doggoned tough now, but it’ll be a darned lot of fun to remember it.
1895		News Herald (Hillsboro, OH) 7 Feb. 3/5: Low and steady, boys [...] and not too doggone high.
1896		P.L. Dunbar ‘An Easy-Goin’ Feller’ in Lyrics of Lowly Life 110: I like to jest be let alone, / To plough my strip an’ tend my bees, / An’ do jest like I doggoned please.
1904		Omaha Dly Bee (NE) 13 Mar. 27/1: Saymister, seein’ you’re so doggone smart, won’t ye [etc.].
1912		Day Book (Chicago) 3 Dec. 10/2: Unofficially the levee was never so doggone dead as some people tried to make out.
1922		S. Lewis Babbitt (1974) 226: I’ll doggone well get my hair cut where I doggone well want to!
1928		N.I. White Amer. Negro Folk-Songs 354: [reported from Auburn, Ala., 1915–1916] He says, ‘The North Pole’s too dog-gonned cold, / I’m Alabama bound.’.
1935		C.G. Finney Circus of Dr Lao 18: How come it’s so doggone yellow?
1943		R. Chandler Lady in the Lake (1952) 83: ‘When you get tired of it, let me know. I’ll have something else.’ ‘I’ll just be doggone sure you will.’.
1953		J. Thompson Alcoholics (1993) 70: I’ll [...] be doggone careful when I drink.
1968		J. Hersey Algiers Motel Incident 22: I can move pretty daggone good if I have to.
1990		S. Morgan Homeboy 69: Doggone no see, long time.
1998		L. Stringer Grand Central Winter (1999) 31: He found that one doggone funny.