Does it seem like your Chicago ancestor’s ward changed often? Did your ancestor move or did the boundaries move? The wards were originally set up as six wards in 1837. By 1921, Chicago was divided up into 50 wards. Between 1851-1931, boundaries were changed as well as wards added ten different times.
The following book details the history and boundaries for each ward:
Centennial list of mayors, city clerks, city attorneys, city treasurers, and aldermen : elected by the people of the City of Chicago, from the incorporation of the City on March 4, 1837 to March 4, 1937, arranged in alphabetical order, showing the years during which each official held office / compiled in commemoration of the centennial of the incorporation of Chicago as a city on March 4, 1937, under the direction of Frederick Rex, Librarian, Municipal Reference Library, City of Chicago.
A transcription of this book is available online courtesy of the Chicago History Museum http://chsmedia.org/media/fa/fa/LIB/AldermansList.htm
Per the title of the book, it also includes a list of mayors, city clerks, city attorneys, city treasurers, and aldermen that were elected from March 4, 1837 to March 4, 1937. At the end, there is an added list of aldermen, city treasurers and city clerks for 1933 to April 1979. Maybe you will be lucky enough to have an ancestor who served in public office for Chicago.