before world war ii, the polish lands were noted for the variety of their ethnic communities. following the polish-soviet war, a large part of its population belonged to national minorities. the census of that year allocates 30.8% of the population in the minority. in 1931, the population of poland was 31,916,000, including 15,428,000 males and 16,488,000 females. by january 1939, the population of poland increased to 35,100,000. this total included 240,000 in zaolzie which was under polish control from october 1938 until august 1939. the population density was 90 persons per square km. in 1921, 24% of the population lived in towns and cities, by 1931 the ratio grew to 27%. altogether, in 1921, there were 611 towns and cities in the country, by 1931 there were 636 municipalities. the six biggest cities of poland (as for january 1, 1939) were warsaw, łódź, lwów, poznań, kraków and vilnius (wilno). in 1931, poland had the second largest jewish population in the world, and one-fifth of all jews resided within poland's borders (approx. 3,136,000, roughly 10% of the entire polish population).