Melt butter in a large skillet and stir in onion, celery, poultry seasoning, black pepper and ½ teaspoon salt. Cook just until tender, about 5 minutes and then cool completely.
Place the dried bread cubes in a greased 6 quart slow cooker. Add cooled onion mixture, parsley, 2 cups of the chicken broth and eggs. Rest 5 minutes.
Add more chicken broth as needed to moisten and gently stir. You may not need all of the broth (see note below).
Turn the slow cooker onto high for 30 minutes. Reduce temperature to low and cook an additional 3-4 hours or until hot and cooked through.
Notes
Store-bought dried bread cubes may require extra broth to moisten.
The broth should be added a little at a time. Depending on the dryness of the bread, not all of the broth may be needed.