Reading on Wikipedia about Polish kings I see paragraphs such as these:

On 9 October 1334, Casimir confirmed the privileges granted to Jews in 1264 by Bolesław V the Chaste. Under penalty of death, he prohibited the kidnapping of Jewish children for the purpose of enforced Christian baptism, and he inflicted heavy punishment for the desecration of Jewish cemeteries. While Jews had lived in Poland since before his reign, Casimir allowed them to settle in Poland in great numbers and protected them as people of the king.[14] Casimir's legendary Jewish mistress Esterka remains unconfirmed by direct historical evidence.[15]

or

Władysław also endeavored to establish a uniform legal code throughout the land. In this code he assured the safety and freedom of Jews and placed them on an equal footing with Christians

Generally unsourced or of dubious quality like news articles. But I often find this idea spread around in pop history media: "Poland was very tolerant Jews, hence there were a lot of Jews in Poland..." where they continue the premise to talk about The Pale of Settlement or the Holocaust. But why? I don't really doubt the claims but I would like some details on the formation of the Polish Jewish community.