Poland is a country referenced and appears in the Wolfenstein series.
It was mentioned as early as some of the original backstory for William Joseph B.J. Blazkowicz in reference to his parents who were originally Polish immigrants from the country. B.J. however was a second generation native/natural born American of the United States either in or near Milwaukee, WI, or near or in Mesquite, TX depending on the timelines.
Poland first appears as a location visited in the games in The New Order.