Tompkins County, New York

[solarstorm]

Tompkins County, NY, is the only county that was not won by Hillary in the 2008 Democratic presidential primary in New York, and not even narrowly (57-40).
It was also Teachout's fourth best county (with >70%) and moreover Wu's second best county in the 2014 Democratic gubernatorial primary.
Does a hippy/hipster community live there? Is it a niche for artists? Or how do you explain those aberrations?

[Adam Griffin]

Probably Cornell University and Ithaca College. Combined, their enrollment makes up about 30% of the county's population (I could be wrong, but it wouldn't surprise me if that's the largest student population as a % of any county in NY).

[Brittain33]

Ithaca is very liberal, and it's not just students.

[The Free North]

Ithaca is very liberal, and it's not just students.

Pretty much this. The universities only enhance the leftward bias of the city

[TDAS04]

Ithaca is a liberal college town.

[bgwah]

Literally 15 seconds of research would have provided you an answer. In fact, this one is so easily explained that you should be banned for even asking.

[ElectionsGuy]

Its one of those small liberal college towns that isn't near a large metropolitan area. Much like Athens, OH or Bloomington, IN.

[Sumner 1868]

Interestingly, it appears the Reagan era was when this area went so Democratic. Before 1984, the only time Tompkins County had voted for a Democratic president was Wilson in 1912 (TR a spoiler) and LBJ in 1964. Since Mondale won in 1984, Democrats have won without much trouble.

[Adam Griffin]

Ithaca is very liberal, and it's not just students.

Pretty much this. The universities only enhance the leftward bias of the city

I'm not sure if this is what you meant by 'enhance', but it's not just in a quantitative fashion. The campuses there surely alter the flavor of leftward thinking to a degree as well (explains the Teachout/Wu/Obama examples pointed out by OP), to the point that even if the county only voted as D as the surrounding ones, it still probably would exude the same tendencies as it does now.