The Poles come from different West Slavic tribes living on territories belonging later to Poland in the early Middle Ages.
Kingdom of Poland (966–1569) Around the year 1000, the population of the Duchy of Poland is estimated at 1,000,000 to 1,250,000. Around 1370 Poland had 2 million inhabitants with a population density of 8.6 per square kilometer. Poland was less affected by the Black Death than Western Europe.
Although the population of the Kingdom of Poland in late Middle Ages consisted mostly of Poles, the influx of other cultures was significant: particularly notable were Jewish and German settlers, who often formed significant minorities or even majorities in urban centers. Sporadically migrants from other places like Scotland, and Netherlands settled in Poland as well. At that time other notable minorities included various incompletely assimilated people from other Slavic tribes (some of whom would eventually merge totally into the Polish people, while others merged into neighboring nations).
Around 1490, the combined population of Poland and Lithuania, in a personal union (the Polish–Lithuanian union) since the Union of Krewo a century before, is estimated at 8 million. An estimate for 1493 gives the combined population of Poland and Lithuania at 7.5 million (including 3.9 million in the Kingdom of Poland), breaking them down by ethnicity at 3.25 million Poles, 3.75 million Ruthenians and 0.5 million Lithuanians. The Ruthenians composed most of the population of the Grand Duchy of Lithuania: this is the reason that the late GDL is often called a Slavic country, alongside Poland, Russia, etc. In time, the adjective "Lithuanian" came to denote a Slav of the Grand Duchy.
Eventually, the Lithuanian speakers came to be known as Samogitians (see also Samogitian nobility), after the province in which they were the dominant majority. Another estimate for the combined population at the beginning of the 16th century gives 7.5 million, roughly split evenly, due to the much larger territory of the Grand Duchy (with about 10-15 people per square km in Poland and 3-5 people per square km in the Grand Duchy, and even less in the south-east Cossack borderlands). By 1500, about 15% of Poland's population lived in urban centers (settlements with over 500 people).
Polish–Lithuanian Commonwealth (1569–1795) By 1600, about 25% of Poland's population lived in urban centers (settlements with over 500 people). Major towns in Poland included: Gdańsk (70,000), Kraków (28,000), Warsaw (20,000-30,000), Poznań (20,000), Lwów (Lviv) (20,000), Elbląg (Elbing) (15,000), Toruń (Thorn) (12,000), Sandomierz (4,000-5,000), Kazimierz Dolny (4,000-5,000) and Gniezno (4,000-5,000).
The population of the Commonwealth of both nations was never overwhelmingly either Roman Catholic or Polish. This resulted from Poland's possession of Ukraine and federation with Lithuania; in both these countries ethnic Poles were a distinct minority. The Commonwealth comprised primarily four nations: Poles, Lithuanians, and Ukrainians and Belarusians (the latter two usually referred to together as Ruthenians), with a considerable amount of the Jews. Shortly after the Union of Lublin (1569), at the turn of the 16th to 17th century, the Commonwealth population was around 7 million, with a rough breakdown of 4.5m Poles, 0.75m Lithuanians, 2m Ruthenians, and 0.7m Jews. In 1618, after the Truce of Deulino the Commonwealth population increased together with its territory, reaching 12 million that could be roughly divided into: Poles – 4.5m, Ukrainians – 3.5m, Belarusians – 1.5m, Lithuanians – 0.75m, Prussians – 0.75m, Jews – 0.5m, Livonians – 0.5m; at that time nobility formed 10% and burghers, 15%. Population losses of 1648–1667 are estimated at 4m. Coupled with further population and territorial losses, by 1717 the Commonwealth population had fallen to 9m: roughly 4.5m Poles, 1.5m Ukrainians, 1.2m Belarusians, 0.8m Lithuanians, 0.5m Jews, 0.5m others The urban population was hit hard, falling to below 10%.
From 1648 to 1660 the Commonwealth lost between 30% and 50% of its population, largely due to the Khmelnytsky Uprising of 1648-1657, the Swedish Deluge, the Polish–Russian War of 1654–1667, and accompanying famines. During the Great Northern War, Poland's population contracted by 25% in 1709–1711.
To be Polish, in the non-Polish lands of the Commonwealth, was then much less an index of ethnicity than of religion and rank; it was a designation largely reserved for the landed noble class (szlachta), which included Poles but also many members of non-Polish origin who converted to Catholicism in increasing numbers with each following generation. For the non-Polish nobility such conversion meant a final step of Polonization that followed the adoption of the Polish language and culture. Poland, as the culturally most advanced part of the Commonwealth, with the royal court, the capital, the largest cities, the second-oldest university in Central Europe (after Prague), and the more liberal and democratic social institutions proved an irresistible magnet for the non-Polish nobility in the Commonwealth.
As a result, in the eastern territories a Polish (or Polonized) aristocracy dominated a peasantry whose great majority was neither Polish nor Roman Catholic. Moreover, the decades of peace brought huge colonization efforts to Ukraine, heightening the tensions among nobles, Jews, Cossacks (traditionally Orthodox), Polish and Ruthenian peasants. The latter, deprived of their native protectors among the Ruthenian nobility, turned for protection to cossacks that facilitated violence that in the end broke the Commonwealth. The tensions were aggravated by conflicts between Eastern Orthodoxy and the Ukrainian Greek Catholic Church following the Union of Brest, overall discrimination of Orthodox religions by dominant Catholicism, and several Cossack uprisings. In the west and north, many cities had sizable German minorities, often belonging to Reformed churches. The Commonwealth had also one of the largest Jewish diasporas in the world.
Until the Reformation, the szlachta were mostly Catholic or Eastern Orthodox. However, many families quickly adopted the Reformed religion. After the Counter-Reformation, when the Roman Catholic Church regained power in Poland, the szlachta became almost exclusively Roman Catholic, despite the fact that Roman Catholicism was not a majority religion (the Roman Catholic and Orthodox churches counted approximately 40% of the population each, while the remaining 20% were Jews and members of various Protestant churches). The Counter-Reformation in Poland, influenced by the Commonwealth tradition of religious tolerance, was based mostly on Jesuit propaganda, and was very peaceful when compared to excesses such as the Thirty Years' War elsewhere in Europe.
In the late 18th century, the first statistical estimates of Commonwealth population appeared. Aleksander Busching estimated the number of Commonwealth population for 8.5 million; Józef Wybicki in 1777 for 5,391,364; Stanisław Staszic in 1785 for 6 million; and Fryderyk Moszyński in 1789 for 7,354,620. Modern estimates tend to be higher; by 1770, on the eve of the partitions, Commonwealth had a population of about 11m-14m, about 10% of that - Jewish. The nobility constituted about 10%, the burghers, about 7-8%.
Partitions (1795–1918) By the First Partition in 1772, the Polish–Lithuanian Commonwealth lost about 211 000 km2 (30% of its territory, amounting at that time to about 733 000 km2), with a population of over four to five million people (about a third of its population of 14 million before the partitions).
After the Second Partition, Commonwealth lost about 307 000 km2, being reduced to 223 000 km2. Only about 4 million people remained in Poland at that time, which makes for a loss of another third of its original population, about a half of the remaining.
After the Third Partition, overall, Austria had gained about 18 percent of the former Commonwealth territory (130,000 km2) and about 32 percent of the population (3.85 million people). Prussia had gained about 20 percent of the former Commonwealth territory 149,000 km2) and about 23 percent of the population (2.6 million people). Russia had gained about 62 percent of the former Commonwealth territory (462,000 km2) and about 45 percent of the population (3.5 million people).
An estimate for 1815 gives 11.5 million Poles, out of which 5m were under Russian control (4 million in Congress Poland and 1 million in the territories incorporated into the Russian Empire), 3.5m in the Prussian partition territories and 3m in the Austrian partition territories.
Congress Poland had a population of about 4.25 million around 1830. In the Russian partition, the Pale of Settlement resulted in resettlement of many Russian Jews to the western fringes of Russian Empire, which now included part of Poland. This further increased the sizable community of Polish Jews. By 1914, about 31 million people inhabited the territories that would become the Second Polish Republic, the First World War saw the population of those territories drop to 26 million.
In the final decades of the 19th century, the Polish-speaking population expanded dramatically – by an estimated 70 to 100 percent – not only due to a very high rate of natural increase, but also due to the voluntary Polonization of non-Poles, a process that occurred particularly in urban areas of Congress Poland and Galicia.
Second Polish Republic and World War II (1918–1945) 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 Trans-Olza 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 of 1 January 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).