William married a fellow Polish immigrant, Michalina Amelia, who came to New York in about 1901. Their wedding photo was provided by family to the biography article. Their marriage was registered twice in May and June of the year 1911, but according to later census records, the couple already had children from around the year 1904. This would mean that Wilkanowski and Amelia either had their first children out of wedlock, or got married any time around 1904, perhaps only registering in a church, as many Catholic Poles would view a church wedding as sufficient for their daily life. She would go by the name Amelia, also registered as Emily or as Emilia (1930 Census). Her maiden name was also listed and misspelled as Glowinska, Growdanska and Grobinska. in New York. Together they seem to have registered 11 children in total, 8 daughters and 3 sons. 9 of their children would survive them – the 7 daughters Helene, Genowefa/Genevieve (1907–1977), Carolyne, Florence, Irene, Viola and Natalie (1924–2009), and the 2 sons Henry (1922–1965) and Theodore Joseph (1919–1969). In the 1940 New York census, Amelia is listed as Emily and 53 years old, 1 year older than William listed as "Wm", 52 years old. Five of their youngest children – the 3 girls and 2 sons – are listed living with the parents in the same 1940 census, which indicates their 5 oldest daughters already moved out and married. The name Joseph seems to have been significant to Wilkanowski, who would also label some of his violins with the name "Juzek", which is the slightly misspelled Polish diminutive of Joseph.