- Ice Cream & Frozen Yogurt, South Portland
- Identification Card Access Services, South Portland
- Identification Equipment, South Portland
- Identification Equipment Supplies & Services, South Portland
- Imported Auto Parts, South Portland
- Indian Restaurants, South Portland
- Industrial & Commercial Cleaning Services & Companies, South Portland
- Industrial & Commercial Real Estate, South Portland
- Industrial & Heavy Equipment Repair & Service, South Portland
- Industrial & Heavy Vehicle Dealers, South Portland
- Industrial Contractors, South Portland
- Industrial Equipment & Machinery, South Portland
- Industrial Goods & Products - Hard Goods - Large, South Portland
- Industrial Goods & Products - Hard Goods - Small, South Portland
- Industrial Goods & Products - Soft - Large & Small, South Portland
- Industrial Heat & Electrical Supplies & Equipment, South Portland
- Industrial Lifts, South Portland
- Industrial Machinery Supplies & Equipment - Leasing & Rental, South Portland
- Industrial Maintenance & Cleaning Contractors, South Portland
- Industrial Pumps, South Portland - Centrifugal, Positive Displacement, Submersible, Diaphragm, Hydraulic, Water, Vacuum Pump, etc
- Industrial Supply, Parts & Equipment - Miscellaneous, South Portland
- Industrial Waste Disposal, South Portland
- Industrial Waste Recycling, South Portland
- Industry, South Portland
- Information Bureaus & Services, South Portland
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- Information Retrieval Services, South Portland
- Information Technology Services, South Portland - IT Service
- Inspection & Testing Services, South Portland
- Insurance Adjusters, South Portland
- Insurance Brokers, South Portland
- Insurance Carriers, South Portland
- Insurance Carriers By Specialty, South Portland
- Insurance Claim Processing Services, South Portland
- Insurance Consultants, South Portland
- Insurance Employee Benefits, South Portland
- Insurance Farm, South Portland
- Insurance General Liability, South Portland
- Insurance Major Medical, South Portland
- Insurance Motorcycles, South Portland
- Insurance Renters, South Portland
- Insurance Services, South Portland
- Insurance Third Party Administrators, South Portland
- Interior Designers, South Portland
- Interior Designers & Decorators, South Portland
- Internet Providers, South Portland
- Internet Services, South Portland
- Inventory Management Services, South Portland - Inventory Service
- Investment Management Services, South Portland
- Investment Services & Advisors, South Portland
- Italian Restaurants, South Portland
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