I spoke too soon. Though the "maybe more" part turns out to have been spot on. The total is now up to 40.
Not all of the companies had released public statements about them dropping the show, but many have. And all did confirm that they were cutting their ads on The O'Reilly Factor.
When Trump proclaimed it "Sexual Assault Awareness Month," who knew that The O'Reilly Factor would take that so literally...
Here's a list of companies that have cut ties.