Green’s Dictionary of Slang

(US) a phr. of asseveration, ‘I declare’.

1823		Missouri Intelligencer 20 May n.p.: I swan it is.
1836		T. Haliburton Clockmaker I 65: If you hante obsarved it, I have, and a queer one it is, I swan.
1839		F.J. Grund Aristocracy in America II v 118: I was glad to find someone to converse with freely, without being every third word stopped by such phrases as these: ‘Why, sir! I don't exactly know;’ [...] ‘I rather guess;’ ‘I should swan,’ (for, ‘I should swear,’) &c.
1840		Jeffersonian Republican (Stroudsburg, PA) 20 Nov. 1/1: I swanny we’ll see what he’s after.
1842		C.M. Kirkland Forest Life I 144: I swan! I’m as lonesome as a catamount!
1843		Jeffersonian Republican (Stroudsburg, PA) 7 June 1/1: Did you ever go up to thanksgiving? I swaggers! what oceans of cakes.
1848		J.R. Lowell Biglow Papers (1880) 115: I used to vote for Martin, but, I swan, I’m clean disgusted.
1852		Woodville Republican (MS) 6 Jan. 1/6: I swanny! this wash hand dish looks jest like marble!
1853		N.Y. Clipper 17 Sept. 4/5: ‘Swan to gracious!’ exclaimed the old contriver.
1862		J.R. Lowell Biglow Papers 2nd ser. (1880) 27: I swan to man, it’s puf’kly indescrib’le.
1875		Alpena Wkly Argus (MI) 5 May 4/1: Well, I swanny, if that ain’t the sarciest boy in town!
1882		Eve. Bulletin (Maysville, KY) 10 Nov. n.p.: His coat — by jockies, it wasn’t hardly long enough to cover his suspenders it wasn’t, I swanny.
1887		G. Davis Recoll. Sea-Wanderer 330: ‘Wall, I swum,'’said the Squire, ‘how time duz fly’ .
1887		‘Lawrence Lynch’ Mountain Mystery 34: ‘Well, I swan!’ ejaculated Podunk. ‘She’d be a bonanza to some man.’.
1897		Argus (Holbrook, AZ) 11 Dec. 8/3: How air ye, Bob? I swanny I’m glad ter see yer.
1905		N.Y. Tribune 12 Feb. 31/1: Oh — he asked you, did he? Well, I swanny!
1909		H. Green Mr. Jackson 1: ‘Well I swan!’ breathed the man wonderingly.
1913		S.F. Call 13 Apr. 9/3: ‘A curiosity, hey ? Wal I swan. What kind of curiosity is it?’ [...] ‘He made a mistake and fetched around a bottle of gasoline, [...] and give it to th’ cow!’ ‘I swanny, no!’.
1921		N.Y. Tribune 30 Jan. 64/1: I swanny if he ain’t counting the money, too, as if he wanted to see how much he was settin’ me back!
1942		Democrat & Chron. (Rochester, NY) 28 May 13: [cartoon caption] Wal, I swan!
1973		S. Ace Stand On It (1979) 52: ‘I swan,’ he says.
2005		D. Jenkins Slim & None 101: ‘You a Democrat? You’re too pretty to be a Democrat.’ ‘George, I’ll swan,’ my mother said.