Currently Illinois is on a stay at home order based on current conditions with covid19. My sons (who has asthma) biological father decided to still go on vacation to Florida. The day he gets back he is supposed to have a 6 hour visit with my son. Am I legally able to deny the visitation in order to make sure my son stays healthy?
You cannot ignore a parent's visitation rights, no matter how strongly you feel about the need to do so. You can (theoretically) file a petition to override those rights, and the court will decide on the merits of your argument, assuming that you have some legal standing in the matter. You would be better off hiring an attorney to make the argument since this is not well-trodden legal grounds – the argument would have to be made that going to Florida is grounds for terminating (even temporarily) his visitation rights. The Illinois order is clear enough that vacation travel is contrary to the order.