Drain clams in a colander over a bowl, reserving juice. Add bottled clam juice to reserved juice to equal 3 1/2 cups. Set aside clams and juice.
Cook bacon in a Dutch oven over medium heat until crisp, stirring occasionally. Remove bacon from pan with a slotted spoon, reserving 2 teaspoons drippings in pan. Return bacon to pan; increase heat to medium-high. Add onion, celery, and butter; sauté 6 minutes or until vegetables are tender.
Add clam juice mixture, potato, and next 4 ingredients (through bay leaf); bring to a boil. Cover, reduce heat, and simmer 15 minutes or until potato is tender. Stir in clams, evaporated milk, 1% milk, and sherry. Cook 5 minutes or until thoroughly heated, stirring occasionally. Discard bay leaf. Sprinkle with parsley.
If fresh clams are available, use about 1 1/2 cups chopped clams.