UPDATE: I had mentioned that I did not believe ggplot2 was the right route for the four panel style presentation but see the R-Bloggers post on how to achieve it with ggplot2 and ggalt. It has been awhile since I have posted a tutorial, or anything for that matter, on my website so I decided to revisit some data from my old post. If you recall in that quick little visualization I just wanted to plot this great new data set.
Below is a tutorial that helps take ZIP code data and, with R, get rough latitude and longitude data from them as well as County. Then using ggplot2 we can create a nice visual of the data plotted at the county level. The first section was written as part of a larger project and I like to keep it around as it was one of the first tutorials on this website.