- 5 Maternity hospitals
- 1 Mathematical instruments
- 1 Mathematics
- 1 Mathew, Theobold 1790-1856
- 1 Mathew's Paper Mill
- 2 Mathews, Charles James, 1803-1878
- 1 Matias Lopez (Firm)
- 1 Matlack & Son Carbon Works
- 1 Matlock Bath, England
- 2 Matricolas
- 1 Matson's Mill
- 1 Matsumae, Japan
- 4 Matsuo-Ehe (Firm)
- 1 Matte's Slaughterhouse
- 1 Matthew & Moore Machine Works
- 14 Matthew, the Apostle, Saint
- 1 Matthews, C. J.
- 2 Matthias, Apostle, Saint
- 2 Mauch Chunk Creek, Pennsylvania
- 4 Maupay's Nursery
- 1 Maurice Fischer's Sons
- 1 Maurice H. Power (Firm)
- 3 Mauritius
- 1 Maverick, P. R. (Peter Rushton), 1755-1811
- 2 Maw & Co.
- 1 Maxentius, Marcus Aurelius Valerius, Emperor of Rome, d. 312
- 4 Maxwell, Mrs.
- 1 Maxwell's Prepared Gypsum Factory
- 1 Mayaud Bros.
- 5 Mayer's Art Institution
- 11 Mayfair, Pennsylvania
- 1 Mayland Mill Dam
- 1 Mayland's Mill
- 24 Mayors
- 1 Maypole Inn
- 1 Maypoles
- 1 Mays Landing, New Jersey
- 1 Mazzini, Giuseppe, 1805-1872
- 3 McAdoo, William Gibbs, 1863-1941
- 26 McArthur, John Jr. (1823-1890), Architect
