Johannis Dahm, the son of Mathias Dahm and Barbara Weinand was born on 23 November 1838 in Welschbillig, Prussia. In the 1900 Federal Census for Niles Township, Cook County, Illinois he stated that he was born in November of 1839, and the rest of the census records confirm that he believed this, however, his birth record clearly shows he was born in November of 1838 with his sister being born in August of 1840. As crazy as it seems, it was not all that uncommon for persons to have not known the year of their birth exactly. He immigrated to the United States from Germany with his parents arriving aboard the Reliance in New York on August 4, 1851. He was sometimes called Johann or John. He died in September 13, 1918 in Chicago, Illinois.
Catherina Gertrude Wagner, the daughter of Johannis Wagner and Elizabeth Jane Heinz. She was born on May 9, 1842, in Fliessem, Kreis Bitburg, Germany, and was baptized the following day at the Heiligkreuz Katholisch. She immigrated to the United States from Germany with her parents in June 3, 1850 arriving aboard the Edwing in New York. She died on September 7, 1904, in Illinois at the age of 62. She had a double funeral service with her son, Jacob. She was buried on September 10, 1904, in St. Peter's Cemetery, in Niles Center, Cook County, Illinois. Catherina was sometimes referred to as Catherine or Katharina.

Johannis and Catharina were married in 1865 had 12 children all born in Niles Center, Cook County, Illinois:

Elizabeth "Eliza" (13 Oct 1866 - 29 Nov 1933) m. 11 Nov 1891, John Ernst Simon (witness for Gerhard Mayer's Natualization)
John J. (1868 - ) m. Anna Gertrude Niles
Mathias M. (3 Apr 1870 - 20 May 1945) m. Margaretha Abbink
Margaretha "Maggie" (21 May 1872 - 18 Feb 1958) [163] m. Gerhard Mayer
Apollonia (14 Sep 1873 - 3 Jan 1960) m. 15 Jan 1902, Jacob Edward Meier
Magdalena Helena (7 Feb 1875 - ) m. 23 Apr 1900, Mathias Thielen
Angela (30 Jul 1876 - ) m. Edward Schlesser
Jacob (16 Jan 1878 - 10 Sep 1904)
Barbara T. (27 Aug 1879 - ) m. Nicholas Schuetz
Gertrude (24 Jan 1882 - 24 Jul 1882)
Catharine (24 Jan 1882 - 2 Mar 1882)
Peter J. (28 Sep 1883 - aft 1910)

The passenger list record for John lists his age as 7 when he was actually 12 years old. The passenger list for Catharina lists her at age 2 when she was 7 or 8 years old.
The 1860 Federal Illinois Census for Niles Center, Cook County, lists John's age incorrectly at 20 years. The 1870 Census, also for Niles Center, lists John's age as 29 years old when he would have actually been 31; Catharina is listed with the correct age of 28 years. The 1880 Census for Niles Center lists John incorrectly at 40 years of age, and Catharina is listed as a year too old at 39 years. The 1900 census for Niles Center lists John's incorrectly as 60 years of age, and Catharina correctly at age 58 years. The 1910 Census for Niles Center lists John's age incorrectly at 70 years of age.