- Dairy Products - Wholesale & Retail, Northport
- Dams, Waterways, & Docks Contractors, Northport
- Dance Companies, Northport
- Dancing Instructions, Northport
- Data Communications Service, Equipment, Supplies & Sales, Northport
- Data Processing Services, Northport
- Day Camps, Northport
- Day Spas, Northport
- Debt Adjusters, Northport
- Decorating & Designing Services, Northport
- Delicatessen Restaurants, Northport
- Dentists, Northport
- Diamonds & Precious & Semi-Precious Stones, Northport
- Diner Restaurants, Northport
- Direct Mail Advertising Services, Northport
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- Dishwashers Sales, Service & Repair, Northport
- Diving Equipment & Supplies, Northport - Scuba & Snorkel Gear & Masks Shops
- Divorce & Family Law Attorneys & Lawyers, Northport
- Doctorate Degree, Northport
- Doctors, Physicians & Surgeons, Northport
- Donuts, Northport
- Drafting Services, Northport
- Drinking Establishments, Northport
- Dry Cleaning & Laundry, Northport - Dry Cleaners
- Dryers Sales, Service & Repair, Northport - Gas & Electric
- Drywall Contractors, Northport - Drywall Repair & Installation Services
- Drywall, Insulation & Plaster Contractors, Northport - Installation & Repair Services
- Durable & Non Durable Goods & Products, Northport
- Dwelling Operators Except Apartment, Northport
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