FCPS has very good early childhood services, including a full-day Preschool Autism Classroom program starting at age 2 for eligible children with that diagnsis. The Child Find offices are located in various centers around the county, assigned to families based on their address.
http://www.fcps.edu/dss/sei/ecids/index.shtml
You can also call the FCPS Parent Resource Center for more information--
http://www.fcps.edu/dss/osp/prc/index.shtml