The following link from ACS says that there should be 3,220 unique counties of any population size presented in a five-year survey. The 1-year only shows those counties with 65,000+ residents.
My file has each of the 5-year ACS files in it. My count of unique counties comes out at 423 (less if I ignore 0000 examples), which is much fewer than 3,220.
That is the same number of counties as when I use the ACS 1-year files. If I understand the ACS page correctly, there should only be 65,000+ counties in the 1-year file, while the 5-year file contains all counties no matter population. As a result the ACS 1-year should not have the same number of counties as the ACS 5-year.
Please help shed some light on this.