- Dairy Products - Wholesale & Retail, Port Jefferson Station
- Dance Companies, Port Jefferson Station
- Data Communications Service, Equipment, Supplies & Sales, Port Jefferson Station
- Day Spas, Port Jefferson Station
- Decorating & Designing Services, Port Jefferson Station
- Delicatessen Restaurants, Port Jefferson Station
- Dental Bonding & Cosmetic Dentistry, Port Jefferson Station - Cosmetic Dentist & Tooth Bonding
- Dentists, Port Jefferson Station
- Department Stores, Port Jefferson Station
- Diner Restaurants, Port Jefferson Station
- Discount Stores, Port Jefferson Station - Clothing, Grocery, Furniture, Etc
- Diving Instruction, Port Jefferson Station
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- Divorce & Family Law Attorneys & Lawyers, Port Jefferson Station
- Doctorate Degree, Port Jefferson Station
- Doctors, Physicians & Surgeons, Port Jefferson Station
- Dogs, Port Jefferson Station
- Donuts, Port Jefferson Station
- Dredging Companies, Port Jefferson Station
- Dressmakers Supplies, Port Jefferson Station
- Drugs, Pharmaceutical Products & Toiletries - Wholesale & Manufacturers, Port Jefferson Station
- Dry Cleaning & Laundry, Port Jefferson Station - Dry Cleaners
- Drywall Contractors, Port Jefferson Station - Drywall Repair & Installation Services
- Dwelling Operators Except Apartment, Port Jefferson Station
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