Green’s Dictionary of Slang

1. (US Und.) a prison known for its liberal regime, or, sarcastically, the opposite.

1975		J. Carr Bad (1995) 141: ‘Disneyland’ is what all the cons call CMC-East. For homos it’s dreams come true.
1984		W. Diehl Hooligans (2003) 51: ‘Graves did a deuce off a nickel in Little Q.’ ‘Little Q?’ ‘Felony Disneyworld,’ said the Stick. ‘A very hard-time joint.’.
1992		Bentley & Corbett Prison Sl. 3: Disneyland An easy prison in which to do time. (Archaic: playhouse).

2. (N.Z. prison) a tablet of LSD, thus in Disneyland, lit. taking an LSD trip, fig. out of mental control.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 56/2: Disneyland n. an LSD tab [...] in Disneyland to be in any situation where one is not in control of one's faculties.