- Sand Gravel & Aggregate, Youngsville
- Sandwich Shop Restaurants, Youngsville
- Scrap & Waste Machinery, Youngsville
- Scrap & Waste Materials, Youngsville
- Screen Printing, Youngsville
- Search & Rescue, Youngsville
- Secondary Schools, Youngsville
- Security & Surveillance System & Equipment, Youngsville
- Security Alarm Systems - Home & Business, Youngsville
- Security Brokers & Dealers, Youngsville
- Security Control Systems & Monitoring, Youngsville - Polygraph, Lie Detector, CCTV, Fire Sensor Equipment, Etc
- Security Services, Youngsville
- Semiconductors & Equipment, Youngsville
- Sheet Metal, Youngsville
- Shopping & Shopping Services, Youngsville
- Sign Hanging & Installation Service, Youngsville - Signs Erectors & Hangers
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- Social Clubs & Organizations, Youngsville
- Social Services & Welfare, Youngsville
- Societies & Foundation Associations, Youngsville
- Solar Energy Research Development & Design, Youngsville
- Special Dies Tools Jigs & Fixtures Manufacturers, Youngsville
- Special Interest Schools Or Instruction, Youngsville
- Specialty Animal Services, Youngsville
- Specialty Stores, Youngsville
- Sporting Goods Stores, Youngsville
- State Government, Youngsville
- Stationery & Office Supplies, Youngsville
- Steel & Metal Goods, Youngsville - Steel Distributors
- Stocks & Bond Brokers, Youngsville
- Stone, Youngsville
- Surplus & Salvage Merchandise, Youngsville
- Surveyor Services, Youngsville - Surveying Service
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