This evaluation of an initial attempt to identify and interpret an economic base classification of county economies finds that (a) measures of the dominant economic base specialties are relatively stable from year to year, (b) a large proportion of counties qualify for at least one specialty class, (c) the overlap is small, (d) the survival probability from prior years to 1979 is very high, (e) the transition probabilities of the descriptors are very high, and (0 there are distinct differences in selected social and economic characteristics of counties in each class. Each of these characteristics is an important part of a county classification system if it is to be used in policy analyses.