I live in Illinois too and having worked for attorneys for many years can offer this advice: As the other reply stated, be sure and print out every e-mail you have from the girlfriend and bio dad. Be sure that you don't say anything that will come back to bite you should you end up in court. As for changing your daughter's last name, that is relatively easy if you were never married to the father. However, if you are very young, and you aren't married now, you may want to consider holding off on that. Later in time, if and when you get married, that would be the time to look into changing your daughter's last name to reflect the love and respect she may have for a step-father that is raising her and so she will have the same last name as you and any future siblings. Is there a child support order in place now? If not, then bio-dad technically doesn't owe any, other than morally. As other people have stated in these forums, child support and visitation are separate issues. If there is a visitation schedule in place, then it should be adhered to under most circumstances even if you aren't getting any child support. If there isn't a visitation schedule in place, wait and let him take you to court to get one. At that time, you can give your attorney all of the evidence you have showing why bio-dad should not have visitation, etc. Keep track of every phone call, e-mail, etc. I do know the name of a family law attorney that is very good, but she costs $$. My DH used her for his divorce and got his kids, his house, his retirement benefits, etc. and they had been married for 19 years. She got visitation every other weekend and one hour a week on Wednesdays for dinners, 2 weeks each summer but not consecutive and she's supposed to pay child support. (Of course she hasn't paid a dime, but we haven't pursued it either).
In the meantime, I would do as much background check on bio-dad and his girlfriend as possible. You'd be surprised how easy it is to do from home. Have they ever been arrested, prior marriages, divorces, children, paying support, living arrangements, employment, lawsuits, etc.
Hope some of this helps. Good luck.