Green’s Dictionary of Slang

an excellent person or thing.

1884		Ariz. Sentinel Yuma Cty, AZ) 19 Dec. 2/3: Planet is the Joe dandy Democrtic precinct in Yuma county.
1887		F. Francis Jr Saddle and Mocassin 312: Well, you may talk about [...] your Smart Alicks, and your Joe-dandies and daisies, but when it comes to making a duck stew, I’m a darling!
1890		Juliaetta Gem 9 Aug. 1/2: Ben is what is termed a ‘Joe dandy,’ and undoubtedly knows how to build grades in a rapid and workmanlike manner [DA].
1899		Wichita Dly Eagle(KS) 9 June 4/1: He must be an intellectual Joe dandy.
1905		Dly Capital Jrnl (Salen, OR) 5 July 2/4: The Reform School band — brass band — is a Jo Dandy.
1906		J. London ‘Brown Wolf’ Complete Short Stories (1993) II 1083: He [i.e. a dog] was a joe-dandy at hammerin’ a raw team into shape.
1913		J. London Valley of the Moon (1914) 352: An’ the horses are Joe-dandies. They know their business as well as a man.
1926		D. Branch Cowboy and His Interpreters 57: Mounted on a ‘cutting pony’ that was a ‘Joe-dandy,’ he made a figure for his boss.