With the name "Prussia" you have to pay attention. I'm born in Buedngen/Upper Hesse and lived in Glauberg where my hessian ancesters can be found until 1676. It never belongs to Prussia, but i found in internettrees of some families, who live now in the USA or Canada, that they write: "Glauberg, Prussia", because non-historicals in America think that Germany was the same as Prussia.
You need a city or village of origin of an ancestor for searching, if the ways of the other two answers didn't work. Or a province of Prussia. Now the following provinces belong to Poland: East-Prussia (Ostpreußen), West-Prussia with Gdansk/Danzig (Westpreußen-Danzig), Pommerania (Pommern, Hinter-Pommern), Poznan/Posen, Silesia/Schlesien (Niederschlesien, Oberschlesien), East-Brandenburg (Brandenburg east of the Oder/Odra).
If you don't have any idea of the origin, perhaps the names of the family can help. Some family names are typical for some regions:
East-Prussia: names endiung on -at, -eit, -uhn, -ies...(perhaps also typical for West-Prussia or Danzig?)
Pommerania, Brandenburg, SIlesia/Schlesien: ending on -ke
Perhaps there are more typical names, but those I found until now. My family name is typical for East Prussia: Albrecht Kauschat
I wish you good luck