However , the city 's population progressively decreased ; in 1920 , it was 7,424 ; in 1930 , it was 6,929 , and in 1940 , it was 6,570 . From there onward , the city 's population progressively decreased : 7,424 in 1920 ; 6,929 in 1930 ; and 6,570 in 1940 .