Harris County, Texas

[Skill and Chance]

An easy plurality of the families in Harris County are directly connected to the oil industry.  That's the main reason.  Also, minority turnout lags other parts of the country.  The other dominant industry is healthcare which does lean left on the whole and there is a traditional urban liberal base.  The county is unusually large geographically and includes a lot of areas that would be considered exurbs in Northeastern setting and vote 75% R.  The city of Houston itself is probably closer to 60/40 D than 50/50.  Imagine if everything within 40 miles of Atlanta were one county.  It's a lot like that.

[Skill and Chance]

Yes, Houston has very conservative suburbs and even exurbs within the county. To give you an idea, here's a screen shot of the county from the 2008 presidential election (by Dave's Redistricting):

Is the label off center or is Sugar Land actually D+low as a town?