fool's paradise

from The American Heritage® Dictionary of the English Language, 4th Edition

• n. A state of delusive contentment or false hope.

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A state of happiness due to illusion or false hope.

from the GNU version of the Collaborative International Dictionary of English

• n. a name applied to a limbo (see under Limbo) popularly believed to be the region of vanity and nonsense. Hence, any foolish pleasure or condition of vain self-satistaction.
• n. See under Fool, and Limbo.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• n. an illusory state of wellbeing