Green’s Dictionary of Slang

(US) a euph. for damned adv.

1825		S. Woodworth Forest Rose I iii: That’s a darnation queer kind of a tune.
1833		C.A. Davis Letters of Major J. Downing (1835) 66: It’s a nasty mean action—and a darnation rascally one too.
1841		Northern Star (Yorks) 18 Sept. 6/5: ‘Darnation cold night, this,’ said the grocer.
1847		Westmorland Gaz. 10 June 3/5: I am darnation glad to hear that.
1850		W.K. Northall Life and Recollections of Yankee Hill 168: I’ve a propensity tew bust rite intew a reglar roar, when I think that a people who looked so ripe as to be yaller, could be so durnation green.
1859		Alice Cary Pictures of Country Life 8: It’s a darnation sight easier.
1864		Leics. Mercury 19 Mar. 2/1: He describes a man as being [...] so darnation ugly.
1870		J.H. Beadle Life in Utah 267: Like dernation well to have a nice, trim, young creatur.
1875		Lancaster Gaz. 22 May 3/1: She is sich a darnation cross critter, she is so cussed contrary.
1887		Manchester Courier 18 June 10/2: Some folks think they’re darnation cute.
1899		Illus. Police News 18 Nov. 5/4: If you’d got a girl with you, you might think darnation true [...] But that Bill would say, ‘I’ll burst if I doesn’t kiss her first’.
1899		London Standard 12 Apr. 8/2: He was that durnation hungry [...] that he had to spend all his pay in buying food.
1905		‘Central Connecticut Word-List’ in DN III:i 7: darnation, adj. and interj. I had a darnation good time.
1909		Manchester Courier 19 Feb. 14/1: Each man’s looking darnation sad.
1931		Eve. Teleg. 28 Apr. 3/7: It was darnation dark, and I cudn’t see nuffin.