Break up turkey carcass to fit 6-quart Dutch oven. Add water, salt, pepper, poultry seasoning and bay leaf. Heat to boiling over high heat; reduce heat to low. Cover; simmer 1 hour 30 minutes.
Skim off any residue that rises to the surface. Remove bones, meat and bay leaf from broth; cool. When cool enough to handle, remove meat from bones and cut into bite-size pieces; set aside. Discard bones and bay leaf.
Skim fat from broth; discard. Add turkey meat cut from bones to broth; stir in barley. Heat to boiling; reduce heat to low. Cover; simmer 30 minutes, stirring occasionally.
Stir in carrots, onion, celery and 3 cups cooked turkey. Simmer uncovered 20 to 25 minutes longer, stirring occasionally, until vegetables and barley are tender. Stir in parsley.