- Tank Cleaning & Draining , Port Jefferson
- Tank Testing & Inspection, Port Jefferson
- Tax Return Preparation, Port Jefferson
- Taxi Cab Service, Port Jefferson
- Taxi Service, Port Jefferson
- Telecommunications, Port Jefferson
- Telecommunications Companies, Businesses & Services, Port Jefferson
- Telephone Answering Service, Port Jefferson - Messenger Services
- Telephone Communication Service & Phone Companies, Port Jefferson - Local & Long Distance Telephone Service
- Telephone Equipment & Phone Systems, Port Jefferson - Sales, Service & Repair
- Television Stores & Dealers, Port Jefferson
- Tennis Courts, Port Jefferson
- Testing Laboratories, Port Jefferson - Lab Tests
- Theater & Sport Ticket Agencies, Port Jefferson
- Theater & Theatrical Supplies & Equipment, Port Jefferson - Stage Lighting, Stage Curtains, Sets, Costumes, etc
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- Theatrical Producers & Services, Port Jefferson
- Thrift Stores, Resale & Consignment Shops, Port Jefferson
- Tires - Wholesale & Retail, Port Jefferson
- Title & Surety Insurance, Port Jefferson
- Title Companies, Port Jefferson - Title Search, Service & Abstract Company
- Towing Service, Port Jefferson
- Toy Stores, Port Jefferson
- Transportation, Port Jefferson
- Transportation Expeditors, Port Jefferson
- Transportation Facilities & Services, Port Jefferson
- Travel & Tourism, Port Jefferson
- Travel Arrangement & Services, Port Jefferson
- Tugboat & Towing Service, Port Jefferson
- Tutoring Instructor, Port Jefferson
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