Just did a little Google research on it. Apparently the number is not known with any degree of certainty. The anti-child support website said that the actual number is a "secret" but it's around 25-50% of all men in county jails.
I suspect that it's no where near a million. Even 250,000 seems high, but that might at least be plausible. The article makes it sound like this is intended to keep GOPers from voting.
I suspect that the overwhelming number of deadbeat fathers are Democrats.
There are a billion (with a b) men in secret jails for not paying child support!