Break up the turkey carcass in a large pot, covering it with water.
Add onion, carrots, and celery. Cover and bring to a boil. Skim any scum from the top.
Reduce heat and simmer uncovered for 2 hours.
Strain soup into another pot, reserving the carcass but discarding the vegetables.
Pick meat from the bones of the carcass.
Return stock to a simmer.
Stir in barley and simmer, covered, for 30 minutes.
Add diced carrots, onion, and turnip. Simmer for 30 minutes or until the vegetables are tender.
Add turkey, salt, and pepper.
