Green’s Dictionary of Slang

loco/loca adj.

(orig. US) insane, crazy.

1887		Outing (N.Y.) X 7/1: You won’t be able to do nuthin’ with ’em, sir; they’ll go plumb loco, that’s what they will .
1895		Yakima Herald (WA) 12 Sept. 4/2: ‘She plumb locoed withj grief,’ says Dan Boggs.
1899		Harper’s New Mthly Mag. 99 612: I think you must be plumb loco to shoot up a lot of men like we be.
1906		Times Dispatch (Richmond, VA) 7 Apr. 6/5: Many of these editors are ‘Locoed’ from hate of anyone who will note instantly obey the ‘demands’ of a labor union.
1907		S.E. White Arizona Nights 153: He looked all right enough, neither drunk nor loco.
1912		D. Lowrie My Life in Prison 332: We did not discover he was ‘loco’ until he had been in jail two days.
1925		D. Hammett ‘Corkscrew’ Story Omnibus (1966) 236: I just went plumb loco.
1931		Don Redmond ‘Shakin’ the African’ 🎵 Gang goes loco, man, / Ever since they started shakin’ that African.
1945		R.S. Close Love me Sailor 258: The bitch was mad — mad as a march hare. Absolutely loco!
1954		Mad mag. Sept. 14: Get lost, squaw! You loco?
1963		G. Lambert Inside Daisy Clover (1966) 16: The Dealer may be loco but she’s no liar.
1977		C. McFadden Serial 66: ‘Isn’t that outrageous?’ ‘Loco’.
1988		Beano Comic Library Special No. 12 1: Lots of your plum loco pals!
1992		Proper Dos ‘First Day of School’ 🎵 on Mexican Power [album] I said ‘You heard the one about the loco cholo going solo?’.
2003		50 Cent ‘In da Club’ 🎵 But holla in New York them niggas’ll tell ya I’m loco.
2008		T. Piccirilli Fever Kill 171: Loco bastard like you.
2018		‘Aidan Truhen’ Price You Pay 28: I could just go loco. Go rogue.
2019		C.D. Rosales Word Is Bone [ebook] ‘Denial makes you crazy [...] Loco. Insane in the brain’.
2023		(con. 1962) J. Ellroy Enchanters 262: ‘I told him Miss Monroe was nice, but she was loca.

In derivatives

locoed (adj.)

1. crazy.

1885		C.A. Siringo Texas Cow Boy (1950) 57: I was too badly ‘locoed’ to tell a good horse from a bad one.
1897		A.H. Lewis Wolfville 14: Whenever a game gets immoderate that a-way, an’ the limit’s off, an’ things is goin’ that locoed they begins to play a thousand an’ over.
1901		S.E. White Westerners 313: He considered the crowd all, as he expressed it, ‘plum locoed’.
1907		S.E. White Arizona Nights II 220: What’s biting the locoed stranger?
1916		H.L. Wilson Somewhere in Red Gap 69: He got so locoed with that song one day.
1926		D. Branch Cowboy and His Interpreters 40: He’s the kind of horse with a far-away look. Some folks call ’em locoed.
1934		O. Strange Sudden 61: Yo’re a cheerful lot o’ locoed pups.
a.1946		‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 116: This locoed vaquero, with spangled sombrero, / Has locoweed under his wig.
1961		L. McMurtry Horseman, Pass By (1997) 79: I believe you’re locoed.
1965		C. Himes Rage in Harlem (1969) 24: They romped towards Abie’s field-cloth like locoed steers.
1978		F.E. Abernethy Paisanos, a Folklore Misc. 7: The rattlesnake suddenly crooks his neck, he’s so plumb locoed with rage an’ fear, an’ socks his fangs into himself.

2. in fig. use, unsteady.

1907

R. Service ‘The Little Old Log Cabin’ in Songs of a Sourdough 57: An’ you’d fancy he’d been boozin’, he’s so locoed ’bout the feet.

In compounds

loco duds (n.) (also loco suit) [duds n.¹ (1)/SE suit]

(US Und.) a strait jacket.

1949

Monteleone Criminal Sl. (rev. edn).