This county has a total area of 6,242 km2 (2,410 sq mi), with mountains occupying about 59% of its surface.

Historically, Alba de Jos County was located in the central-western part of Greater Romania, in the southwestern part of Transylvania, with a territory identical with the old Alsó-Fehér County of Hungary.

According to the census data of 1930, the county's population was 212,749, of which 81.5% were Romanians, 11.3% Hungarians, 3.6% Germans, 1.8% Romanies, 1.4% Jews, as well as other minorities.

[9] In 1930, the urban population of the county was 33,365, of which 58.8% were Romanians, 23.0% Hungarians, 8.2% Germans, 6.2% Jews, 1.6% Romanies, as well as other minorities.

From the religious point of view, the urban population was made up of 38.3% Eastern Orthodox, 21.4% Greek Catholic, 14.7% Reformed (Calvinist), 7.2% Evangelical (Lutheran), 6.5% Jewish, as well as other minorities.