Gayle, you raise an interesting question.
The short answer: >from everywhere, throughout the Middle Ages. The
generally accepted view is that, although there are records of Jews in
Poland as early as the 10th century CE, the main influx was >from Western
Europe, mainly the Rhineland, in the wake of the crusades and mass
expulsions in the 13th and 14th centuries. However, many (including, I
think, my MILLET ancestors) came to Galitzia >from the Ottoman Empire in
the 15th and 16th centuries, and an unknown number came west >from
the Khazar Empire much earlier, after it fell in the 11th century. It's even
possible - though there's no evidence - that some English Jews might have
found their way to Poland after the expulsion of 1290.
BTW the highlight of the JGS-GB 1-day con in London last Sunday was our
own Pamela Weisberger's fascinating talk on Gesher Galicia!
Best wishes and happy ancestor-spotting,
Richard Cooper (NB: Not related to any COOPERs!)
MILLET, ENGELBERG, BLUMENKEHL, SUSSWEIN, WACKS & PITERZIL >from
Tarnow, Dabrowa Tarnowska and Lezajsk; LEZTER, SALENDER, RINENBERG,
EISEN & KRAETTER >from Rzeszow and Kolbuszowa; ADLER, FINKELSTEIN,
PARYLLE, WEINTRAUB & ZILZ >from Tarnopol and Trembowla; YAROSHEVSKY,
SHAPOCHNIKOW & GRANITUR >from Odessa and Zlatopol/Novomirgorod;
LEWINSTEIN >from Berdichev; BORENSTEIN, MATELEVITCH,GODZINSKIJ &
ZIMNOWICZ and >from Warsaw and Radun