Seeking surname Slovick

My grandmother came from Bohemia in 1881 with her parents and some or all of her 5 sisters according to my aunt who still had a great memory 15 years ago. They settled in St Paul, MN and eventually in Todd County, MN. They are listed in census records with the surname Slovick. Their family name may have been changed by immigration officials or the family themselves.

I am sure that the family was:
Frederick (b. 1850) and Josephine (b. 1851) – parents
Anna, Kate, Josephine, Emma, Agnes (1873 – 1973), and Frances (1878 – 1929) Daughters
Charles, the only son was born in Minnesota

I want to establish the family surname and link the family to their town / village in the Czech Republic