According to Kazimierz Rymut (Rymut, Kazimierz. 2003. Dictionary of surnames in current use in Poland at the beginning of the 21st century. Chicago, Il: Polish Genealogical Society of America.), in Poland at the beginning of the 21st century, the distribution of the Niedzialkowski surname and its variants included:

Niedzialkowska - 3
Niedzialkowski - 2
Niedzialkowska - 809
Niedzialkowski - 786

The Niedzialkowska surname is most frequently found in the following locations in Poland:

Warszawa - 72
Lipno - 39
City of Wloclawek -33
Ciechanów - 31
Aleksandrów Kujawski - 27
Plonsk - 24)
Minsk Mazowiecki - 20
Maków Mazowiecki - 19
Sierpc - 18
Przasnysz - 17

The Niedzialkowski surname is most frequently found in the following locations in Poland:

Warszawa - 55
Ciechanów - 35
Lipno - 30
Plonsk - 27
Minsk Mazowiecki - 24
City of Wloclawek - 22
Aleksandrów Kujawski - 19
Przasnysz - 16
Pultusk - 16
Szczecin - 16

In the United States, many immigrants with the Niedzialkowski surname modified or anglicized the name. Some of the variants include:

Niedzialkowski
Niedzialkowsky
Niedzialkoski
Niedzialkosky
Niedzial
Cosky
Sunday
Newman

The US Federal Census shows that, in 1930, individuals with the Niedzialkowski surname resided in the following states:

Connecticut
Massachusetts
Michigan
Missouri
New Jersey
New York
Ohio
Pennsylvania
Wisconsin