Child support when the father works under the table
I live in Illinois and want to know how the court orders and determines child support when the father works under the table and there is no paper trail of his income. He is currently paying $100 weekly for his daughter but it is not court ordered and he wants nothing to do with a court order, however he is not always consistent and goes 2 months at a time without paying. I know generally what he makes but without verification of his income ( he pays no taxes), how would the court decide what is fair? Should I make an attempt to document him working?