The Locks on the C&O Canal, located in Maryland, West Virginia, and Washington, D.C. of the United States, were numbered from 1 to 75 with two locks, 63⅓ and 64⅔, having fractional numbers and no lock 65. There is also a lock at the downstream end of the canal in Washington, DC where Rock Creek flows into the Potomac River which is sometimes called Lock 0 or the Tidewater Lock.
Some of the locks were also informally named, usually after a prominent lockkeeper, a nearby town or important geographical feature. Some locks are known by more than one name and some are only known by their number.
With respect to the fractional locks, it was found that the level of the canal between locks 62 and 66 could be raised in three steps instead of four. So the additional locks through there were numbered 1⅓ steps apart (62, 63⅓, 64⅔ and 66) so that the other locks on the canal did not have to be renumbered.
| Lock | Miles | Name | Nearby landmarks | Coordinates |
|---|---|---|---|---|
| 0 | 0.0 | Tidewater Lock | ||
| 1 | 0.38 | Georgetown | ||
| 2 | 0.42 | Georgetown | ||
| 3 | 0.49 | Georgetown | ||
| 4 | 0.54 | Georgetown | ||
| 5 | 5.0 | Brookmont Lock | Brookmont | |
| 6 | 5.4 | Magazine Lock | Little Falls | |
| 7 | 7.0 | Chataqua Lock | Glen Echo | |
| 8 | 8.33 | Seven Locks 1 | ||
| 9 | 8.7 | Seven Locks 2 | ||
| 10 | 8.79 | Seven Locks 3 | ||
| 11 | 8.97 | Seven Locks 4 | ||
| 12 | 9.29 | Seven Locks 5 | ||
| 13 | 9.37 | Seven Locks 6 | American Legion (Cabin John) Bridge | |
| 14 | 9.47 | Seven Locks 7 | ||
| 15 | 13.45 | Six Locks 1 | Great Falls | |
| 16 | 13.60 | Six Locks 2 | Great Falls | |
| 17 | 13.99 | Six Locks 3 | Great Falls | |
| 18 | 13.99 | Six Locks 4 | Great Falls | |
| 19 | 14.17 | Six Locks 5 | Great Falls | |
| 20 | 14.30 | Six Locks 6 - aka Tavern Lock | Great Falls Tavern | |
| 21 | 16.64 | Swain's Lock | ||
| 22 | 19.63 | Pennyfield Lock | ||
| 23 | 22.12 | Violette's Lock and Inlet Lock 2 | ||
| 24 | 23.00 | Riley's Lock | Seneca Creek Aqueduct | |
| 25 | 30.8 | Edward's Ferry | Poolesville | |
| 26 | 39.4 | Wood's Lock | ||
| 27 | 41.5 | Spinks Ferry | Monocacy Aqueduct | |
| 28 | 48.9 | Fulton's Lock | Point of Rocks | |
| 29 | 50.89 | Lander Lock or Catoctin Lock | ||
| 30 | 55.0 | Brunswick, Maryland | ||
| 31 | 58.0 | Weverton Lock | ||
| 32 | 60.23 | Sandy Hook, Maryland | ||
| 33 | 60.7 | Harper's Ferry | ||
| 34 | 61.57 | Goodheart's Lock | Harper's Ferry | |
| 35 | 62.33 | Harper's Ferry | ||
| 36 | 62.44 | Harper's Ferry | ||
| 37 | 66.96 | Mountain Lock | ||
| 38 | 72.65 | Shepherdstown Lock | Shepherdstown, West Virginia | |
| 39 | 74.0 | One Mile Lock | James Rumsey Bridge, Snyder's Landing | |
| 40 | 79.41 | Horseshoe Bend | ||
| 41 | 88.9 | |||
| 42 | 89.04 | |||
| 43 | 92.96 | |||
| 44 | 99.3 | Williamsport | Williamsport, Maryland | |
| 45 | 107.27 | Two Locks 1 | ||
| 46 | 107.42 | Two Locks 2 | ||
| 47 | 108.8 | Four Locks 1 | ||
| 48 | 108.8 | Four Locks 2 | ||
| 49 | 108.8 | Four Locks 3 | ||
| 50 | 108.8 | Four Locks 4 | ||
| 51 | 122.59 | Hancock 1 | Hancock, Maryland | |
| 52 | 122.85 | Hancock 2 | Hancock, Maryland | |
| 53 | 130.0 | Irishman's Lock | Leopard's Mill | |
| 54 | 134.0 | |||
| 55 | 134.0 | Near Dam 6 | ||
| 56 | 136.2 | Sideling Lock | Sideling Hill | |
| 57 | 139.2 | |||
| 58 | 143.9 | |||
| 59 | 146.6 | |||
| 60 | 149.7 | Stickpile Hill | ||
| 61 | 153.1 | |||
| 62 | 154.2 | |||
| 63⅓ | 154.5 | Paw Paw Tunnel | ||
| 64⅔ | 154.6 | |||
| 66 | 154.7 | |||
| 67 | 161.8 | Darkey's Lock | ||
| 68 | 164.8 | Crabtree's Lock | ||
| 69 | 166.4 | Twigg's Lock | ||
| 70 | 166.7 | Oldtown | ||
| 71 | 167.0 | |||
| 72 | 174.4 | The Narrows or Ten Mile Lock | ||
| 73 | 175.4 | North Branch 1 | ||
| 74 | 175.5 | North Branch 2 | ||
| 75 | 175.6 | North Branch 3 | ||
| 184.5 | End of the canal | Cumberland, Maryland |