Green’s Dictionary of Slang

judy n.²

(orig. US) a fool; usu. in phr. below.

c.1815		J.K. Paulding Bucktails (1847) V vii: What a Judy you are, governor.
1824		Atlantic Mag. i 346: Wot are ye laughin’ at, ye judies [F&H].
1945		J.B. McMillan ‘New American Lexical Evidence’ in AS XX:1 112: Judy, n. A foolish, silly person.

In phrases

make a Judy (Fitzsimmons) (mother) of oneself (v.)

to be a fool, to make an idiot of oneself.

1781		‘Buac’ aill lion deuc’’ in Bullfinch 82: But you won’t make a Judy of Dennis O’Neal. / With your jumping, jungling, grinning, mouthing, / Clout-headed, thick-headed, brazen-nos’d, copper-fac’d, / Ill looking thief!
1788		Morris et al. ‘Dennis O’Neal’ in Festival of Anacreon (1810) 76: [as 1781].
1831		Satirist (London) 24 Apr. 19/2: [M]y lady swore [...] he should not—make a Judy of himself. (Judy [...] is sign-on-a-mouse with nincompoop, a Greek word for wisdom).
1837		‘Terence O’Shaughnessy’ in Bentley’s Misc. Jan. 43: Just going to make a Judy Fitzsimmons mother of yourself?
1842		S. Lover Handy Andy 367: To say nothing of the constant annoyance of his mother’s growling at him for making ‘such a judy’ of himself.
1845		D. Corcoran Pickings from N.O. Picayune (1847) 21: Don’t be makin’ a Judy Fitzimmons of yerself.
1858		‘Philip Paxton’ Piney Woods Tavern 68: They [a group of men] was up and a stirrin’ I tell you; they called a meetin’, and they made a chairman and seketarie, and passed resolutions, and made perticklar Judies of themselves ginerally.
1859		W.H. Maxwell Erin-go-bragh 215: ‘Why, what have I done ? What am I about doing?’ I demanded. ‘Just going,’ returned Mrs. O'Finn, ‘to make a Judy Fitzsimmons mother of yourself!’.
1874		Harper’s Mag. XLIX 158/2: Don’t make a Judy of yourself, and let that old padded-up major cut you out.
1895		Mirror of Life 17 Aug. 11/1: ‘Making a Judy Fitzsimmons mother of yourself’ is an Irish expression, which, interpreted, means making a fool of yourself.