The following explanation of the meaning of "Wolniewicz" is taken from an email from my father, Dr. Richard (Wally) Wolniewicz, in 1997. This email was part of a discussion among a number of Wolniewicz's on the web.
Wolnosc is the Polish word for the concept "freedom" and wolny is the adjectival form of free. According to the Dictionary of Surnames, Wolniewicz is the patronymic form of Wolniak, which means one who has been freed from the obligations of serfdom. The Dictionary of Surnames states that Wolniak is one of the most common names in Poland and among Americans of Polish descent. It is roughly translated to English as "Freeman". Wolniak is common in other Slavic countries and languages and has Yiddish derivatives as well. Tomasz's words suggest that the patronymic of Wolniak was rarely formed outside the Poznan region in Poland.
The patronymic form wicz means "son of" in Polish and has close equivalents in all Slavic languages as well as other variants in other languages, e.g., Petersen in Norwegian or Mac in Scottish. MacGregor, e.g., means children of Gregor.
I am not surprised and happy to learn that the name Wolniewicz is common to the Poznan area. My own family is reported to come from the small village of Rypin, not far from Torun and Bydgoszcz, which are not too distant from Poznan city. The only other point of reference I had was a photographer whose mother had the same name and was from Bialystok, which is in the northeast lake district. According to numbers I saw about ten years ago, only nineteen (19) families in the United States had the name Wolniewicz. So a person could count the numbers of Wolniewicz families in the United states on both hand and feet. A few were clustered around Connecticut.