US place GEOID
The seven-digit geographic identifier of a US place, composed by the Census Bureau from the state and place codes.
Seven digits: the two-digit state followed by a five-digit place code. Aaronsburg, Pennsylvania is 4200100.
A place is either an incorporated city, town, borough or village, or a Census Designated Place, which is the statistical counterpart the Bureau delineates for a named settlement that state law never incorporated. Both kinds share this code, so the code alone does not say whether a place has a government.
Places belong to states rather than to counties and may cross a county line, which is why a place code is never built from a county code. Place codes were assigned alphabetically within each state when first issued, so gaps and out-of-sequence values are normal today.