- Occupational Health & Safety, Stratford
- Occupational Health Care Professionals, Stratford
- Occupational Therapy, Stratford - Occupational Health Specialists
- Office Buildings & Parks, Stratford
- Office Supplies, Equipment & Office Furniture Stores, Stratford
- Oil Burners, Stratford
- Oil Change & Lubrication, Stratford - Auto Oil & Quick Lube
- Ophthalmologists, Stratford - Eye Doctors, Physicians & Surgeons (Ophthalmology)
- Optical Goods Manufacturers, Stratford
- Optical Stores - Eyeglasses, Lenses & Sunglasses, Stratford
- Opticians, Stratford
- Optometrists, Stratford - Eye Doctors, Physicians & Surgeons (Optometry)
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- Ornamental Nursery, Stratford
- Ornamental Nursery Services, Stratford
- Orthodontist, Stratford - Teeth Straightening, Invisalign & Dental Braces
- Orthopedic & Prosthetic Appliances & Shoes, Stratford - Orthopedic Shoes
- Orthopedists, Stratford - Orthopedic Surgery Doctors, Physicians & Surgeons
- Osteoporosis Doctors, Stratford - Physicians & Surgeons
- Other Building Materials & Supplies, Stratford
- Outdoor & Lawn & Garden Equipment Repair & Service, Stratford
- Outdoor Equipment & Accessories, Stratford
- Overhead Door, Stratford
- Ownership Organizations, Stratford
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