I am attempting to to calculate the percentage distribution of income by quintile in 2000 for a number of counties in and around NYC. I was attempting to use the the PUM files I found here http://www2.census.gov/acs/downloads/pums/2000/ to do so, and was able to use them to calculate those quintile percentages for the states of NY, NJ and CT as a whole, but I couldn't figure out how to separate out the data in them by counties or any other geographic sub-division. Is there a way to separate the data in those files by county or other regions, or are their other files I need in order to do so and where could I find them?