The article asserts - "So where have people been moving to...Generally to southern Sun Belt states"

If you compute absolute population growth from 1969 to 2011 on a per-county basis, using publicly available demographic stats, the top-20 winners are

     ----
     Arizona        Mohave        7.38100563286945
     Georgia        Paulding        7.4570788900017675
     Virginia        Loudoun        7.954704312171496
     Georgia        Henry        8.023498694516972
     Texas        Hood        8.128975265017667
     Florida        Collier        8.313786154239164
     Texas        Denton        8.504770344932634
     Georgia        Fayette        8.909350004596856
     Texas        Montgomery        9.526487258446021
     Utah        Washington        10.029741513547181
     Florida        Hernando        10.384018414995067
     Georgia        Forsyth        10.637015231025215
     Florida        Osceola        10.880533448053345
     Texas        Rockwall        10.907133440749963
     Georgia        Gwinnett        11.063892016788289
     Texas        Fort Bend        11.168507788849015
     Texas        Williamson        11.323119312014695
     Colorado        Summit        11.39344262295082
     Texas        Collin        11.507137247655564
     Florida        Flagler        21.135939986360537
     Colorado        Douglas        36.49576488706366
     ------

So Douglas county in Colorado grew the fastest, 3600% growth! Indeed, it had a population of about 8000 folks in 1969 & now averages about 300000 => thats your 3600%

Generally speaking, the South is a big winner - GA, TX, FL, AZ...

3139 counties ranked by population growth in my github repo here - http://bit.ly/16RsjWa

Here's some Scala code for crunching this data yourself : http://bit.ly/1hZDQny