The first census carried out in the Polish Republic was that of 30 September 1921, and on that date there were 27,176,700 residents, 70 per sq. Km. The second census took place on December 9, 1931 and gave a population of 32,120,000 residents, 82.2 per sq. Km.; an evaluation as of January 1934 gave 33,024,000 residents. In the decade 1921-1931, therefore, the population of Poland increased on average by 18.2 ‰ per year (in the territory already under Russian rule in the period 1867-1885 the increase was as much as 22 ‰). This increase is very strong, among the largest, indeed, occurred in European countries, and is particularly high in the eastern voivodships, where the population is partly made up of Ruthenians, White Russians and Lithuanians and where the surplus of births on dead: since the population increase in Poland is essentially due to natural growth. In the five-year period 1919-1923 per 1000 residents there were 33.3 live births and 22.3 deaths (surplus of 11); in the following two five years, 1924-1928 and 1929-1933, the births were respectively 33.3 and 29.9 ‰, the dead 17.2 and 15.4 ‰ (excess of 16.1 and 14, 5 ‰). The annual average of marriages per 1000 residents it was 11.3% in the period 1919-1923, and it was 8.9 in 1929-1933 (maximum in the southern voivodeships, 9.2). Both nuptiality, birth rate and mortality tend to decrease: fortunately, more pronounced decrease in mortality, due to the much improved health conditions. The voivodships where natural population growth is lower are those of southern Poland, who have the highest mortality rate (17.1 ‰ in 1929-1933; Lentro 14.9, East 15, West 14) and do not reach the birth rate of Eastern voivodeships (30.2 and 33.2 respectively ‰; voivodeships of the center 29.1, of the west 27.5). Overall, both the birth rate and the mortality are decreasing as we proceed from east to west. For the natural growth of the population, Poland is in one of the first places among the European countries, being surpassed only by Russia, Bulgaria and Yugoslavia. The strong population increase that occurred between 1921 and 1931 as well as survival was caused by the repatriation of a large number of people who, due to the war, had had to leave Polish territory (refugees, prisoners, etc.): between 1919 and in 1925 they were repatriated 1.

According to agooddir, before the World War the territories that now constitute the Polish Republic were one of the major European centers of emigration, both transoceanic and continental. The data we have in this regard are not very reliable, because in the statistics the Poles were often counted together with the Russians or the Germans, depending on whether they came from the territories subject to Russia, Germany or Austria, sometimes, then, they were considered separately Jewish or Ruthenian emigrants from Polish territory. However, it can be assumed that between 1900 and 1914, on average, about 100,000 Poles emigrated annually to transoceanic countries, as well as a very considerable number of Jews and Ruthenians. 80-85% of the emigrants went to the United States, the rest went to settle in Canada, Argentina and Brazil. In the period 1899-1914, the annual average of Poles who emigrated to the United States was 87,700. This transoceanic emigration was largely permanent, because repatriations from those distant countries fluctuated, according to the years, between 12 and 32%. On the other hand, continental emigration was temporary, directed above all to Germany (90% of the total, which was approximately 600,000 individuals annually), followed at a great distance by Denmark. Germany welcomed every year – for a few months – from 300 to 440 thousand Poles and from 60 to 120 thousand Ruthenians residents in Polish territory. To all this we must add emigration to other regions of the Russian Empire, which was also considerable (in 1914 the Poles who lived outside Poland in Russian territories were estimated at 700,000).

After the war and the constitution of Poland in an independent state, there was a radical change in both continental and transoceanic emigration. This was reduced to a third of the pre-war figure by the limitations imposed by the United States, which, as mentioned, they absorbed almost ⁹ / ₁₀, by the changes brought by immigration policy from other American countries, the devaluation of the Polish currency, the increase in transport costs. Germany, which absorbed the ⁹ / ₁₀ of continental emigration, in the last few years it has not only not offered more work to Polish workers, but has also repatriated those who had lived there for many years or forced them to look for work in other countries. Thus, from 1919, there was an emigration towards France, still considerable in 1933. The migratory current towards Palestine, made up exclusively of Jews, is also remarkable. Overall continental emigration has decreased by ¼ compared to the pre-war figures, and can be said to have ceased to Germany and Denmark. The decrease in emigration is not due only to the reasons mentioned above, of an external nature, but also to reasons of an internal nature: agrarian reform, development of the legislation protecting labor, increase in industries, etc.

After the proclamation of independence, the number of repatriations has naturally risen, and exceeds 50%. Between 1926 and 1930, 964,100 people emigrated from Poland, of which 679,100 went to European countries (285,100 in France, 362,600 in Germany, etc.) and 285,000 to non-European countries (42,700 in the United States, 103,700 in Canada, 119,600 in America. Southern, 12,300 in Palestine, etc.). In 1933 the emigration was only 35,500 people (76,000 in 1931, 21,400 in 1932), of which 11,400 went to France, 10,300 to Palestine, 3800 to South America, 1300 to the United States, 1100 to Canada. Emigration to Germany barely exceeded 700 people. Repatriations were 459,700 in the five-year period 1926-1930 (of which 426,500 from European countries and of these 320,200 from Germany alone), 87.

Poles are variously estimated between 28 and 30 million, of whom 22,000,000 live in Poland, and the remainder are subjects of other states, in territories adjacent to the mother country or forming ethnic islands in the midst of different populations; or they reside as immigrants in other European and American states. Of the Poles living outside the borders of the country, 3,342,200 are in the United States (of which 1,268,600 were born in Poland, and the rest in the United States), 782,300 in the USSR (especially in Ukraine and White Russia), 310,000 in France, 259,800 in Germany, 120,000 in Brazil, 82,000 in Romania, 81,000 in Czechoslovakia, 58,000 in Lithuania, 57,000 in Latvia, 12,000 in the territory of the Free City of Gdansk, etc. Also noteworthy are the nuclei of Poles living in Canada and Argentina.

According to Polish sources, 1,370,000 Poles live in the USSR (almost double those given by Soviet statistics), 250,000 in Czechoslovakia, 240,000 in Lithuania, etc.: and the total number of Poles would rise to 29 or 30 million.