| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| O-hirota | city | Niigata | Japan | 37.35 | 138.67 | 328 | 22666 |
| Oakasawa | city | Niigata | Japan | 36.88 | 138.64 | 2624 | 1316 |
| Obanaji | city | Niigata | Japan | 37.70 | 139.39 | 328 | 2764 |
| Obazawa | city | Niigata | Japan | 38.25 | 139.53 | 164 | 27268 |
| Obiori | city | Niigata | Japan | 37.57 | 138.92 | 124 | 51050 |
| Obiro | city | Niigata | Japan | 37.29 | 138.98 | 830 | 9950 |
| Obuchi | city | Niigata | Japan | 37.90 | 139.14 | 3 | 150472 |
| Oda | city | Niigata | Japan | 37.91 | 138.48 | 0 | 3675 |
| Odaira | city | Niigata | Japan | 37.15 | 138.52 | 984 | 4826 |
| Odomari | city | Niigata | Japan | 37.83 | 138.33 | 3 | 4712 |
| Ogata | city | Niigata | Japan | 37.92 | 139.12 | 3 | 191793 |
| Ogata-honcho | city | Niigata | Japan | 37.92 | 139.12 | 3 | 191793 |
| Ogi | city | Niigata | Japan | 37.81 | 138.26 | 0 | 4602 |
| Ogi | city | Niigata | Japan | 37.82 | 138.27 | 3 | 5062 |
| Ogi | city | Niigata | Japan | 37.51 | 138.71 | 164 | 10973 |
| Ogi-kaneta-shinden | city | Niigata | Japan | 37.83 | 138.25 | 370 | 4426 |
| Ogi-kinoura | city | Niigata | Japan | 37.83 | 138.28 | 134 | 5474 |
| Ogi-kowashimizu | city | Niigata | Japan | 37.81 | 138.23 | 0 | 3481 |
| Ogi-oura | city | Niigata | Japan | 37.84 | 138.25 | 328 | 4545 |
| Ogibori | city | Niigata | Japan | 37.57 | 139.03 | 167 | 25801 |
| Ogimachi | city | Niigata | Japan | 37.82 | 138.27 | 3 | 5062 |
| Ogishiro | city | Niigata | Japan | 37.51 | 138.71 | 164 | 10973 |
| Ogoto | city | Niigata | Japan | 38.43 | 139.59 | 902 | 2248 |
| Ogunimachi-ainohara | city | Niigata | Japan | 37.29 | 138.69 | 321 | 8810 |
| Ogunimachi-aramachi | city | Niigata | Japan | 37.29 | 138.71 | 328 | 9429 |
| Ogunimachi-nanokamachi | city | Niigata | Japan | 37.32 | 138.71 | 328 | 11073 |
| Ogunimachi-nihon'yanagi | city | Niigata | Japan | 37.29 | 138.70 | 318 | 8495 |
| Ogunimachi-nihon’yanagi | city | Niigata | Japan | 37.29 | 138.70 | 318 | 8495 |
| Ogunimachi-ogai | city | Niigata | Japan | 37.24 | 138.71 | 830 | 7410 |
| Ogunimachi-yamanota | city | Niigata | Japan | 37.25 | 138.68 | 830 | 7177 |
| Ohirota | city | Niigata | Japan | 37.35 | 138.67 | 328 | 22666 |
| Ohmi | city | Niigata | Japan | 37.02 | 137.80 | 830 | 8496 |
| Ohosuto | city | Niigata | Japan | 38.34 | 139.56 | 328 | 752 |
| Okanomachi | city | Niigata | Japan | 37.22 | 138.64 | 830 | 6522 |
| Okashinden | city | Niigata | Japan | 37.87 | 139.21 | 13 | 49690 |
| Okemi | city | Niigata | Japan | 36.90 | 138.25 | 1968 | 4264 |
| Okura | city | Niigata | Japan | 37.15 | 138.98 | 1669 | 13731 |
| Okutsu | city | Niigata | Japan | 37.65 | 138.87 | 22 | 53908 |
| Omata | city | Niigata | Japan | 38.51 | 139.60 | 830 | 3300 |
| Omi | city | Niigata | Japan | 38.10 | 139.55 | 246 | 2064 |
| Omi | city | Niigata | Japan | 37.02 | 137.80 | 830 | 8496 |
| Omokura | city | Niigata | Japan | 37.60 | 139.50 | 984 | 1716 |
| Onadani | city | Niigata | Japan | 37.25 | 138.55 | 830 | 10915 |
| Ono | city | Niigata | Japan | 37.00 | 137.87 | 328 | 14331 |
| Onomi | city | Niigata | Japan | 38.21 | 138.36 | 830 | 2710 |
| Oritate-matashinden | city | Niigata | Japan | 37.20 | 139.06 | 1099 | 3991 |
| Osaki | city | Niigata | Japan | 37.62 | 138.99 | 95 | 91142 |
| Osaki | city | Niigata | Japan | 37.13 | 138.95 | 830 | 18356 |
| Oshima | city | Niigata | Japan | 38.10 | 139.52 | 249 | 6801 |
| Oshima | city | Niigata | Japan | 37.12 | 138.50 | 830 | 4745 |
| Osudo | city | Niigata | Japan | 38.34 | 139.56 | 328 | 752 |
| Ota | city | Niigata | Japan | 37.91 | 138.48 | 0 | 3675 |
| Ota-shinden | city | Niigata | Japan | 36.96 | 138.67 | 1824 | 6981 |
| Otaki | city | Niigata | Japan | 36.91 | 138.16 | 2624 | 3693 |
| Otani | city | Niigata | Japan | 36.91 | 138.23 | 1850 | 4180 |
| Otoji | city | Niigata | Japan | 37.92 | 139.31 | 111 | 35015 |
| Otomo | city | Niigata | Japan | 37.56 | 138.73 | 154 | 9139 |
| Owarino | city | Niigata | Japan | 37.01 | 138.65 | 853 | 9362 |
| Oyamada | city | Niigata | Japan | 37.73 | 139.24 | 262 | 27295 |
| Oyuki | city | Niigata | Japan | 38.35 | 139.55 | 308 | 471 |