Gerhard Mayer was the son of Johannis Mayer and Catherine Reicherts. He was born on June 1, 1864, in Germany. He died on February 8, 1949, in Chicago, Cook County, Illinois. Gerhard immigrated to the United States from Germany in May of 1892 . He may have been from Vittledorf, Germany (S. Bolivia).
According to her certificate of baptism dated June 2, 1872 and occuring in St. Peter's Catholic Church, in Niles Center, Cook County, Illinois, Margaretha Dahm was the daughter of Johannis Dahm and Catharina Wagner and was born May 21, 1872. Margaret was confirmed on 11 June, 1888. She died on February 18, 1958, in Chicago, Cook County, Illinois. She was called Maggie.
Gerhard and Maggie were married on February 12, 1896, in Cook County, Illinois, presumedly in Chicago.

Gerhard and Maggie had 5 children:
Catharine Josephine (1896 - 1896)
Susan Angela (23 Feb 1898 - 1 Jun 1932) m. John "Jack" Hensler (Children: Mary, John A., Robert John, Susan (m. Bob Busch))
Clara Elizabeth (3 Jun 1900 - 26 Apr 1983) m. Fredrick Albert Loebach
John A. (~1903 - ) m. Viola Greiner (Children: Johnny b. ~1936 and twin boys)
Ernest Gerhard/A. "Ernie" (13 Jun 1906 - 11 May 1975) m. 23 Jun 1934, Katherine L. "Kay" O'Rourke (Children: John Robert "Jackie" b. ~1934 and Nancy Kay b. 18 Jan 1938)

Ernie was undoubtedly named after Ernst Simon who married Maggie's oldest sister and was a witness on Gerhard's naturalization.

Gerhard owned and operated a grocery store in Chicago, Illinois. Maggie was a seamstress. They owned a 6 flat on Edgewater Avenue. Their daughter Clara and family lived in the apartment above them. The other 4 apartments were rented out.

In 1914 a John Mayer is listed as a witness on Gerhard Mayer's naturalization record. This John Mayer was living seperately, so could not be his son who would have been at the most 16 years old. This John Mayer may have been a brother. He was born in 1858 and immigrated in 1883. Gerhard named his first son John as well. Probably this older John Mayer is an oldest son, and their father was named John.

[URL: https://vitacollections.ca/IllinoisNews/details.asp?ID=3469609&n=12]
Notes for Ernest A. Mayer
Spouse: Katherine
Survived by: Three sons, John R. Mayer of Chicago, Gerard F. Mayer of Miami, FL, and James M. Mayer of Boston, MA; daughter, Nancy Kay Mayer of Evanston; sister, Clara Loebach of Chicago; and two grandchildren.
Age 68.
Cemetery: All Saints Cemetery, Des Plaines
Date of Publication : 15 May 1975
Date Of Event : May 11, 1975

https://vitacollections.ca/IllinoisNews/details.asp?ID=1660565&n=3
Katherine O'Rourke Mayer, 90, of Evanston, formerly of Wilmette, born in Minonk, Illinois, died November 21, 1998. Survivors include one daughter, Nancy Kay Mayer of Evanston; three sons, John R. , James M. (Kristine) and Gerard F. (Betsy) of North Barrington; one grandchild; and one sister, Mary Seguin. Preceded in death by her husband, Ernest A. Mayer
Date of Publication
26 Nov 1998

PeopleFinder, etc. -
Nancy Kay Mayer 83 (2020) Evanston, IL
Relatives:
Gerard F Mayer (? His birth date was listed as 01.23.48)
James Michael Mayer (? He was born on January 22, 1948. lives Barrington, IL)
Katherine O Mayer