I don't know for sure Rifke, but it might be a result of a great number of immigrants coming from The Netherlands during the early fifties of the previous century.
I know, in that time, more than 100.000 immigrants left their country, going to mainly, the United States, Canada and Australia.
Many people here have as part of their last name the suffix van, or like in Belgium, Van.
In stead of using the first name people got used to be called Van and so it developed as a first name.
Don't know anything about Dutch roots of Van Williams.