| Morristown National Historic Park | Morris | New Jersey | - | - | - | - | 10/26/2010 |
| Moro Creek Bottoms Natural Area | Calhoun | Arkansas | 133.06 | 128.62 | 12.77 | 10.99 | 04/17/2014 |
| Morgan Hill State Forest | Cortland | New York | 106.86 | - | 1.60 | - | 05/20/2017 |
| Morehouse Lake Rd. | Hamilton | New York | - | - | - | - | 09/26/2015 |
| Moreau Lake State Park | Saratoga | New York | 117.36 | 114.20 | 8.80 | 7.38 | 05/17/2020 |
| Montpelier Estate Landmark Forest | Orange | Virginia | 147.06 | 134.70 | 9.75 | 7.28 | 12/12/2019 |
| Montpelier - Plantation House Trees | Orange | Virginia | 97.86 | 89.15 | 15.10 | 12.84 | 10/17/2005 |
| Montpelier - Landmark Forest | Orange | Virginia | 144.54 | 135.07 | 15.49 | 12.14 | 12/30/2009 |
| Montgomery Woods State Nature Preserve | Mendocino | California | - | - | - | - | 06/25/2019 |
| Montgomery Place Historic Estate | Dutchess | New York | 123.12 | - | 10.23 | - | 04/08/2019 |
| Montgomery Place | Dutchess | New York | - | - | - | - | 03/17/2019 |
| Montgomery Bell State Park | Dickson | Tennessee | 144.20 | 137.49 | 10.88 | 9.84 | 01/02/2026 |
| Montezuma's Well | Yavapai | Arizona | 59.54 | - | 8.15 | - | 02/28/2012 |
| Montepulciano | Provincia Di Siena | Tuscany | - | - | - | - | 09/17/2017 |
| Montana Single Tree Sites | Lewis And Clark | Montana | - | - | - | - | 01/01/2000 |
| Mont Clare Cliffs And Schuykill River Corridor | Montgomery | Pennsylvania | 120.56 | 112.84 | 13.22 | 11.20 | 05/25/2009 |
| Monarch Pass | Chaffee | Colorado | - | - | - | - | 06/20/2023 |
| Mokelumne Wilderness | Alpine | California | - | - | - | - | 08/02/2014 |
| Mohican Memorial State Park | Ashland | Ohio | - | - | - | - | 11/17/2013 |
| Mohawk Trail State Forest | Franklin | Massachusetts | 123.14 | - | 7.56 | - | 08/19/2013 |
| Mizpah Campground | Clear Creek | Colorado | - | - | - | - | 08/15/2006 |
| Missouri Botanical Garden | St. Louis | Missouri | 76.06 | 55.76 | 9.96 | 6.98 | 05/20/2018 |
| Mississippi Single Tree Sites | Hinds | Mississippi | 76.02 | - | 8.98 | - | 01/01/2001 |
| Mission Hospital Hawthorns | Buncombe | North Carolina | - | - | - | - | 02/06/2008 |
| Minnesota Single Tree Sites | Ramsey | Minnesota | - | - | - | - | 01/01/2000 |
| Mingus Mountain | Yavapai | Arizona | 43.08 | - | 5.41 | - | 03/08/2012 |
| Mingus Creek | Swain | North Carolina | 151.08 | 143.50 | 10.52 | 8.24 | 04/30/2007 |
| Mingo Creek County Park | Washington | Pennsylvania | 127.60 | 122.95 | 16.77 | 14.80 | 10/24/2011 |
| Millstone Creek Area | Elk | Pennsylvania | 111.16 | 100.00 | 12.68 | 10.15 | 04/24/2008 |
| Mill Stream Run Reservation | Cuyahoga | Ohio | 115.16 | 109.63 | 10.30 | 8.50 | 12/26/2011 |
| Mill Creek Park, Youngstown, OH | Mahoning | Ohio | 123.14 | 115.88 | 8.77 | 6.13 | 07/13/2003 |
| Middleton Place Home And Gardens | Dorchester | South Carolina | 110.42 | 97.63 | 10.36 | 5.18 | 10/11/2012 |
| Middleton Estate | Montgomery | Pennsylvania | - | - | - | - | 11/22/2008 |
| Middle Prong Wilderness | Haywood | North Carolina | 54.86 | - | 6.57 | - | 07/24/2006 |
| Middle Fork Of Snoqualamie River | King | Washington | - | - | - | - | 11/15/2016 |
| Middle Fork Of Salmon River Corridor-Dagger Falls To Confluence Of Salmon River | Valley, Custer, Lemhi, Idaho | Idaho | 89.10 | - | 8.20 | - | 07/01/2011 |
| Middle Fork Of Gila River | Grant | New Mexico | - | - | - | - | 09/19/2009 |
| Michigan Single Tree Sites | Ingham | Michigan | - | - | - | - | 01/01/2001 |
| Michael P. Yellick Conservation Area | Worcester | Massachusetts | - | - | - | - | 04/03/2017 |
| Mianus River Gorge Preserve | Westchester | New York | 118.84 | - | 0.00 | - | 10/17/2016 |
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