- Laboratories Dental, East Setauket
- Laboratories Medical, East Setauket
- Landscape Contractors & Designers, East Setauket
- Landscape Garden Services, East Setauket
- Landscaping, East Setauket
- Landscaping Materials & Supplies, East Setauket
- Laser Printers, East Setauket - Office Supplies
- Lawn & Garden Equipment & Supplies, East Setauket
- Lawn & Garden Services, East Setauket
- Lawn Maintenance Services, East Setauket
- Lawn Mowers & Power Equipment, East Setauket
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- Lawyers & Attorneys, East Setauket
- Legal Professionals, East Setauket
- Libraries, East Setauket
- Life Insurance, East Setauket
- Liquor Stores, East Setauket
- Locks, East Setauket
- Locksmiths, East Setauket - Residence, Commercial, Safe & Auto Car Locksmith
- Locksmiths Equipment & Supplies, East Setauket
- Long Haul Trucking Companies, East Setauket
- Lutheran Church, East Setauket
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