| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| Olacin | city | Maryland | United States | 39.41 | -77.36 | 351 | |
| Old Annapolis Neck | city | Maryland | United States | 38.94 | -76.49 | 22 | |
| Old Baltimore | city | Maryland | United States | 39.41 | -76.24 | 3 | |
| Old Bayside | city | Maryland | United States | 38.68 | -76.55 | 98 | |
| Old Cedar Point | city | Maryland | United States | 38.93 | -76.53 | 3 | |
| Old Colony | city | Maryland | United States | 38.53 | -76.97 | 147 | |
| Old Colony Cove | city | Maryland | United States | 38.73 | -76.55 | 36 | |
| Old County Estates | city | Maryland | United States | 39.06 | -76.53 | 98 | |
| Old Dixie Manor | city | Maryland | United States | 39.57 | -76.36 | 830 | |
| Old Farm | city | Maryland | United States | 39.05 | -77.14 | 298 | |
| Old Farm | city | Maryland | United States | 39.45 | -77.44 | 341 | |
| Old Field Point | city | Maryland | United States | 39.52 | -75.90 | 0 | |
| Old Fields | city | Maryland | United States | 39.55 | -76.36 | 393 | |
| Old Ford Hills | city | Maryland | United States | 38.74 | -76.97 | 127 | |
| Old Fort Acres | city | Maryland | United States | 38.73 | -76.97 | 88 | |
| Old Georgetown Estates | city | Maryland | United States | 39.05 | -77.13 | 324 | |
| Old Germantown | city | Maryland | United States | 39.16 | -77.28 | 410 | |
| Old Glory Beach | city | Maryland | United States | 39.15 | -76.55 | 3 | |
| Old Hickory | city | Maryland | United States | 38.35 | -76.44 | 42 | |
| Old Home Estates | city | Maryland | United States | 39.43 | -76.94 | 830 | |
| Old House Cove Estates | city | Maryland | United States | 38.34 | -76.44 | 29 | |
| Old Line Village of Fair Hill | city | Maryland | United States | 39.72 | -75.89 | 308 | |
| Old Mill | city | Maryland | United States | 39.12 | -76.62 | 98 | |
| Old Mill Bottom Estates | city | Maryland | United States | 39.02 | -76.46 | 49 | |
| Old Orchard Estates | city | Maryland | United States | 39.30 | -77.31 | 830 | |
| Old Point Estates | city | Maryland | United States | 38.94 | -76.29 | 0 | |
| Old Salem Village | city | Maryland | United States | 39.09 | -77.01 | 400 | |
| Old Severna Park | city | Maryland | United States | 39.07 | -76.55 | 0 | |
| Old Sycamore Estates | city | Maryland | United States | 38.45 | -76.87 | 147 | |
| Old Town | city | Maryland | United States | 39.14 | -76.11 | 3 | |
| Old Town | city | Maryland | United States | 39.29 | -76.61 | 6 | |
| Old Town Bowie | city | Maryland | United States | 39.00 | -76.78 | 98 | |
| Old Villa | city | Maryland | United States | 38.80 | -76.11 | 3 | |
| Old York Manor | city | Maryland | United States | 39.52 | -76.58 | 830 | |
| Old York Manor | city | Maryland | United States | 39.65 | -76.56 | 830 | |
| Olde Mill | city | Maryland | United States | 38.46 | -76.57 | 98 | |
| Olde Mill Estates | city | Maryland | United States | 39.38 | -76.77 | 830 | |
| Olde Oak Run | city | Maryland | United States | 39.42 | -77.12 | 830 | |
| Olde Washington Valley | city | Maryland | United States | 39.46 | -77.01 | 830 | |
| Oldfield | city | Maryland | United States | 39.50 | -77.19 | 830 | |
| Oldfield | city | Maryland | United States | 38.60 | -76.52 | 52 | |
| Oldfield Acres | city | Maryland | United States | 39.55 | -75.88 | 3 | |
| Oldtown | city | Maryland | United States | 39.54 | -78.61 | 830 | |
| Olive | city | Maryland | United States | 39.33 | -77.58 | 400 | |
| Oliver Beach | city | Maryland | United States | 39.37 | -76.34 | 3 | |
| Olivet | city | Maryland | United States | 38.34 | -76.44 | 3 | |
| Olivet Hill | city | Maryland | United States | 39.34 | -75.87 | 49 | |
| Olney | city | Maryland | United States | 39.15 | -77.07 | 830 | |
| Olney Acres | city | Maryland | United States | 39.15 | -77.09 | 830 | |
| Olney Estates | city | Maryland | United States | 39.15 | -77.05 | 830 | |
| Olney Mill | city | Maryland | United States | 39.18 | -77.07 | 830 | |
| Olney Oaks | city | Maryland | United States | 39.15 | -77.08 | 830 | |
| Olney Square | city | Maryland | United States | 39.16 | -77.08 | 830 | |
| Olney Town | city | Maryland | United States | 39.16 | -77.07 | 830 |