- Safety Training Schools, Chelmsford
- Sand Gravel & Aggregate, Chelmsford
- Sandwich Shop Restaurants, Chelmsford
- Secondary Schools, Chelmsford
- Security Brokers & Dealers, Chelmsford
- Senior Citizens Service & Health Organizations, Chelmsford
- Sewing & Yarn Stores & Supplies, Chelmsford
- Sharpening Service, Chelmsford
- Shopping & Shopping Services, Chelmsford
- Siding Contractors, Chelmsford - Vinyl Siding, Wood, Metal & Aluminum Siding Contractors - Installation & Repair
- Ski & Snowmobile Clubs, Chelmsford
- Small Appliances, Chelmsford
- Snacks & Desserts, Chelmsford
- Social Services & Welfare, Chelmsford
- Societies & Foundation Associations, Chelmsford
- Sod & Sodding Service, Chelmsford
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- Soil Testing Labs, Chelmsford - Concrete Testing
- Solar Equipment, Chelmsford
- Special Coatings, Chelmsford - Protective Coatings
- Special Events Photographers, Chelmsford
- Special Interest Schools Or Instruction, Chelmsford
- Speciality Food Stores, Chelmsford
- Specialty Animal Services, Chelmsford
- Specialty Stores, Chelmsford
- Sporting Goods Equipment Rental, Chelmsford
- Sporting Goods Stores, Chelmsford
- Sports & Recreational Services, Chelmsford
- Staffing & Support Services, Chelmsford
- Steel & Metal Goods, Chelmsford - Steel Distributors
- Steel Manufacturers, Chelmsford
- Stoves & Furnace Equipment, Chelmsford - Fittings & Repair Parts
- Submarine Sandwich Restaurants, Chelmsford
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