- Machine Shop, Northumberland
- Machine Shop & Tool Repair Service, Northumberland
- Machinery, Supplies & Equipment - Business Production Related, Northumberland
- Machinery, Supplies & Equipment - Business Supplies Related, Northumberland
- Machinery, Supplies & Equipment - Construction & Contractor Related, Northumberland
- Manicurists & Pedicurists, Northumberland
- Manufacturing, Northumberland
- Masonry Materials & Supplies, Northumberland
- Meat Market, Wholesale & Products, Northumberland
- Medical Supplies & Equipment, Northumberland
- Membership Sports & Recreation Clubs, Northumberland
- Metaphysical Churches, Northumberland
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- Methodist Church, Northumberland
- Mexican Restaurants, Northumberland
- Mining, Northumberland
- Miscellaneous Government, Northumberland
- Miscellaneous Manufacturing, Northumberland
- Miscellaneous Professional, Northumberland
- Modular & Mobile Homes For Sale, Northumberland - Manufactured Homes Sale & Service
- Moldings Materials, Northumberland
- Motor Vehicle, Northumberland
- Music, Northumberland
- Musical Instruments & Equipment Stores, Northumberland
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