If my delinquent state taxes have been sold to a collection agency, can I include them in a bankruptcy filing?

You can try to include them in the filing, but you need to be prepared that you may not be able to discharge them. Perhaps not surprisingly, the government--which is what authorizes bankruptcy--has decided to not let people use bankruptcy to get out of paying their governmental debts. Many tax debts, therefore, even if sold to collection agency, are not dischargeable in bankruptcy--bankruptcy will not make them go away. It  may be worth consulting with a bankruptcy attorney to confirm whether or not bankruptcy will help you, but as stated, there is a good chance it will not. Here is a link to a government website that provides some good, basic information about bankruptcy: http://www.uscourts.gov/FederalCourts/Bankruptcy/BankruptcyBasics.aspx.