I am trying to create an heat map animation that shows how a metric changes over time by county in the U.S. Can someone point me to a library for working with county maps and displaying/animating metrics in this way?

So the structure of my data will be:

state   county  year  month  metric
MN    Dakota  2009    1       0.0345
MN    Dakota  2009    2       0.0499
...
...


for all counties in the U.S.