Do you mean Lipka Tatars? Yes, they were (mostly) Muslims serving in the army of Polish-Lithuanian Commonwealth and had been settled there. But not really that

Do you mean Lipka Tatars? Yes, they were (mostly) Muslims serving in the army of Polish-Lithuanian Commonwealth and had been settled there. But not really that many of them - 2 thousand according to 2011 cenzus. Their villages (at least only those two remaining within in Polish border) still have mosques. https://en.wikipedia.org/wiki/Lipka_Tatars https://en.wikipedia.org/wiki/Lipka_Tatars