My grandfather's name was James Paul Cajka. He was born May 10, 1907 in Austria. He lived in the Lorain, Ohio area most of his life (where I'm originally from). In his obituary (9/15/1990), it lists brothers Stanley (Avon Lake), John, Joseph, and three sisters Elizabeth, Anna, and Mary.
I don't come across many other Cajkas either even where we lived in Ohio. I was told that it was Slovak as well when I was growing up, so you're most likely right. Nice hearing from you!