Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Orchard Beach Volunteer Fire Company 11 | Building | | Anne Arundel | 39 18 28 N | 076 55 02 W |
| Orchard Creek | Bay | 0 | Worcester | 38 16 30 N | 075 11 13 W |
| Orchard Estates | Populated Place | 201 | Washington | 39 40 20 N | 077 35 51 W |
| Orchard Gate at Piney Orchard | Populated Place | 66 | Anne Arundel | 39 04 25 N | 076 42 44 W |
| Orchard Grove Elementary School | School | 98 | Frederick | 39 23 33 N | 077 26 17 W |
| Orchard Hill | Populated Place | 18 | Kent | 39 13 10 N | 076 05 49 W |
| Orchard Hills | Populated Place | 115 | Baltimore | 39 25 03 N | 076 37 16 W |
| Orchard Hills | Populated Place | 197 | Washington | 39 41 20 N | 077 43 31 W |
| Orchard Hills Elementary School | School | 108 | Baltimore | 39 25 01 N | 076 37 25 W |
| Orchard Lakes | Populated Place | 168 | Harford | 39 32 03 N | 076 28 59 W |
| Orchard Park | Park | 128 | Montgomery | 39 07 14 N | 077 15 43 W |
| Orchard Place (subdivision) | Populated Place | 130 | Montgomery | 39 08 12 N | 077 13 42 W |
| Orchard Point | Cape | 1 | Anne Arundel | 39 07 25 N | 076 26 50 W |
| Orchard Point | Cape | 1 | Kent | 39 07 07 N | 076 09 54 W |
| Orchard Point | Cape | 0 | Kent | 39 08 15 N | 076 08 47 W |
| Orchard Point | Cape | 13 | St. Mary's | 38 10 51 N | 076 26 55 W |
| Orchard Point at Piney Orchard | Populated Place | 62 | Anne Arundel | 39 04 08 N | 076 42 29 W |
| Orchard Pond (subdivision) | Populated Place | 130 | Montgomery | 39 08 45 N | 077 13 27 W |
| Orchard Ridge | Ridge | 0 | Somerset | 37 59 40 N | 076 02 41 W |
| Orchard Ridge | Ridge | 223 | Washington | 39 42 07 N | 078 03 50 W |
| Orchard Ridge Cemetery | Cemetery | 212 | Washington | 39 41 09 N | 078 05 02 W |
| Orchard Ridge Methodist Church | Church | 212 | Washington | 39 41 08 N | 078 05 02 W |
| Orchard Ridge Park | Park | 135 | Montgomery | 39 04 10 N | 077 10 07 W |
| Orchard Valley Farms | Locale | 147 | Harford | 39 39 03 N | 076 28 44 W |
| Orchard View | Populated Place | 122 | Cecil | 39 40 35 N | 076 04 59 W |
| Orchard View | Populated Place | 30 | Prince George's | 39 01 45 N | 076 54 26 W |
| Orchard View | Populated Place | 19 | Queen Anne's | 39 01 58 N | 076 02 05 W |
| Orchards Branch | Stream | | Kent | 39 15 02 N | 076 12 18 W |
| Orchards of Linthicum | Populated Place | 51 | Anne Arundel | 39 12 25 N | 076 39 18 W |
| Orchardview Estates | Populated Place | 107 | Harford | 39 33 22 N | 076 08 13 W |
| Ordinary Point | Cape | 0 | Cecil | 39 22 17 N | 075 58 47 W |
| Oregon | Populated Place | 112 | Baltimore | 39 29 50 N | 076 41 11 W |
| Oregon Branch | Stream | | Baltimore | 39 29 00 N | 076 39 13 W |
| Oregon Industrial Park | Locale | 11 | Anne Arundel | 39 13 40 N | 076 39 39 W |
| Oregon Ore Bank | Mine | 125 | Baltimore | 39 29 32 N | 076 41 18 W |
| Oregon Pool | Lake | 120 | Baltimore | 39 29 34 N | 076 41 17 W |
| Oregon Ridge Park | Park | 167 | Baltimore | 39 29 03 N | 076 41 38 W |
| Oregon Ridge Swimming Club (historical) | Locale | 120 | Baltimore | 39 29 34 N | 076 41 18 W |
| Oregon School (historical) | School | 138 | Carroll | 39 38 21 N | 077 08 44 W |
| Orem Middle School | School | 31 | Prince George's | 38 57 51 N | 076 57 37 W |
| Orems Church | Church | 22 | Baltimore | 39 19 51 N | 076 27 17 W |
| Orems School | School | 25 | Baltimore | 39 19 59 N | 076 27 49 W |
| Oriole | Populated Place | 1 | Somerset | 38 10 23 N | 075 48 28 W |
| Oriole Cemetery | Cemetery | 1 | Somerset | 38 10 23 N | 075 47 51 W |
| Oriole Park at Camden Yards | Locale | 11 | Baltimore (city) | 39 17 01 N | 076 37 18 W |
| Oriole Post Office | Post Office | 1 | Somerset | 38 10 27 N | 075 48 49 W |
| Orleans Volunteer Fire Company | Building | | Allegany | 40 09 51 N | 078 38 17 W |
| Orme | Populated Place | 61 | Prince George's | 38 38 33 N | 076 45 56 W |
| Orme School | School | 57 | Prince George's | 38 38 04 N | 076 45 23 W |
| Orr Acres | Populated Place | 18 | Anne Arundel | 39 07 50 N | 076 30 24 W |
| Osborne | Populated Place | 24 | Harford | 39 32 12 N | 076 07 02 W |
| Osborne Heights | Populated Place | 36 | Anne Arundel | 39 11 05 N | 076 38 59 W |
| Osborne Shopping Center | Locale | 25 | Prince George's | 38 47 02 N | 076 47 48 W |
| Osborns Ruins | Populated Place | 20 | Harford | 39 27 27 N | 076 17 04 W |
| Otter Creek | Channel | 4 | Somerset | 38 00 40 N | 075 59 20 W |
| Otter Island | Island | 0 | Somerset | 37 58 11 N | 075 59 34 W |
| Otter Point | Cape | 2 | Cecil | 39 36 00 N | 075 50 40 W |
| Otter Point | Cape | 3 | Harford | 39 26 47 N | 076 15 59 W |
| Otter Point | Cape | 0 | St. Mary's | 38 07 03 N | 076 20 38 W |
| Otter Point Creek | Stream | | Harford | 39 26 46 N | 076 14 37 W |
| Otter Pond | Lake | 4 | Anne Arundel | 39 04 17 N | 076 25 51 W |
| Otter Pond | Lake | -4 | Dorchester | 38 23 50 N | 076 04 25 W |
| Otter Pond Branch | Stream | | Dorchester | 38 28 56 N | 075 52 55 W |
| Otterbein Chapel Cemetery | Cemetery | 280 | Frederick | 39 42 27 N | 077 25 57 W |
| Otterbein Chapel United Brethren Church (historical) | Church | 280 | Frederick | 39 42 26 N | 077 25 58 W |
| Otterbein Memorial United Brethren in Christ Church | Church | 93 | Baltimore (city) | 39 20 03 N | 076 37 59 W |
| Otterbein United Brethren Church (historical) | Church | 164 | Washington | 39 38 22 N | 077 43 08 W |
| Otterbein United Methodist Church | Church | 164 | Washington | 39 38 32 N | 077 42 59 W |
| Otterdale Mill | Populated Place | 124 | Carroll | 39 36 58 N | 077 10 01 W |
| Ottersdale | Populated Place | 155 | Carroll | 39 37 54 N | 077 10 00 W |
| Ottersdale School (historical) | School | 159 | Carroll | 39 37 55 N | 077 09 58 W |
| Otwell Woodland Preserve | Park | 2 | Talbot | 38 42 10 N | 076 07 24 W |
| Our Fathers House | Locale | 818 | Garrett | 39 25 49 N | 079 16 53 W |
| Our Lady Help of Christians Church | Church | 61 | Charles | 38 36 15 N | 076 54 36 W |
| Our Lady of Fatima Roman Catholic Church | Church | 32 | Baltimore (city) | 39 17 28 N | 076 32 22 W |
| Our Lady of Fatima School | School | 35 | Baltimore (city) | 39 17 27 N | 076 32 21 W |
| Our Lady of Good Counsel Catholic Church | Church | 2 | Dorchester | 38 36 37 N | 075 57 05 W |
| Our Lady of Good Counsel High School | School | 142 | Montgomery | 39 02 44 N | 077 03 06 W |
| Our Lady of Good Counsel Roman Catholic Church | Church | 6 | Baltimore (city) | 39 16 08 N | 076 35 34 W |
| Our Lady of Good Counsel School | School | 6 | Baltimore (city) | 39 16 08 N | 076 35 35 W |
| Our Lady of Hope School | School | 9 | Baltimore | 39 16 06 N | 076 29 28 W |
| Our Lady of Lourdes Catholic Church | Church | 121 | Baltimore (city) | 39 19 34 N | 076 40 26 W |
| Our Lady of Lourdes Church | Church | 107 | Montgomery | 38 59 07 N | 077 05 30 W |
| Our Lady of Lourdes School | School | 121 | Baltimore (city) | 39 19 34 N | 076 40 26 W |
| Our Lady of Lourdes School | School | 104 | Montgomery | 38 59 08 N | 077 05 27 W |
| Our Lady of Mercy Catholic Church | Church | 78 | Montgomery | 39 00 34 N | 077 10 27 W |
| Our Lady of Perpetual Help Catholic Church | Church | 16 | Anne Arundel | 38 54 38 N | 076 32 29 W |
| Our Lady of Perpetual Help Parish | Church | 147 | Howard | 39 14 18 N | 076 46 05 W |
| Our Lady of Perpetual Help School | School | 132 | Baltimore | 39 19 19 N | 076 45 22 W |
| Our Lady of Pompeis Roman Catholic Church | Church | 25 | Baltimore (city) | 39 17 23 N | 076 34 02 W |
| Our Lady of Pompeis School | School | 25 | Baltimore (city) | 39 17 24 N | 076 34 02 W |
| Our Lady of Sorrows Catholic Church | Church | 47 | Prince George's | 38 58 39 N | 076 59 28 W |
| Our Lady of Sorrows Roman Catholic Church | Church | 37 | Anne Arundel | 38 50 52 N | 076 35 57 W |
| Our Lady of Sorrows School | School | 46 | Prince George's | 38 58 38 N | 076 59 26 W |
| Our Lady of the Field Cemetery | Cemetery | 49 | Anne Arundel | 39 03 04 N | 076 39 02 W |
| Our Lady of the Fields Roman Catholic Church | Church | 50 | Anne Arundel | 39 03 03 N | 076 39 03 W |
| Our Lady of the Wayside Church | Church | 10 | St. Mary's | 38 22 01 N | 076 46 38 W |
| Our Lady of Victory Church | Church | 41 | Baltimore (city) | 39 16 26 N | 076 40 15 W |
| Our Lady of Victory Roman Catholic Church | Church | 54 | Baltimore | 39 16 01 N | 076 41 48 W |
| Our Lady of Victory School | School | 54 | Baltimore | 39 16 02 N | 076 41 47 W |
| Our Lady Queen of Angels Church | Church | 45 | Prince George's | 38 54 09 N | 076 43 02 W |
| Our Lady Queen of Peace School | School | 33 | Baltimore | 39 21 21 N | 076 25 49 W |
| Our Lady Star of the Sea Roman Catholic Church | Church | 0 | Calvert | 38 19 30 N | 076 27 37 W |
| Our Lady Star of the Sea School | School | 0 | Calvert | 38 19 30 N | 076 27 36 W |
| Our Ladys Chapel | Church | 3 | St. Mary's | 38 15 40 N | 076 37 14 W |
| Our Ladys Chapel Cemetery | Cemetery | 1 | St. Mary's | 38 15 38 N | 076 37 16 W |
| Our Ladys Manor | Locale | 6 | Charles | 38 17 19 N | 076 50 46 W |
| Our Savior Lutheran Church | Church | 18 | Charles | 38 36 00 N | 077 07 51 W |
| Our Savior Lutheran Church | Church | 50 | Prince George's | 39 04 38 N | 076 50 54 W |
| Our Savior Lutheran Church | Church | 81 | Prince George's | 38 49 19 N | 076 57 23 W |