| O'Donoghue's Terrace, Woodquay | — | 6 |
| O'Flaherty Road, Shantalla | — | 7 |
| O'Keeffe Park, Glenamaddy | — | 5 |
| Oakfield, Oranmore | — | 9 |
| Oakfield Estate, Oranmore | €332,000 | 17 |
| Oaklands, Salthill | — | 14 |
| Oakwood, Athenry | €226,250 | 8 |
| Oakwood, Ballindereen | — | 17 |
| Oakwood View, St Josephs Rd | — | 5 |
| Ocean Drive, Coast Road | — | 13 |
| Ocean Drive, Oranmore | €735,000 | 11 |
| Ocean Towers, Salthill | — | 9 |
| Ocean Wave, Dr. Colohan Road | — | 13 |
| Ocean Wave, Salthill | €550,000 | 29 |
| Oceanwave, Salthill | — | 5 |
| Old Church Street, Athenry | — | 8 |
| Old Galway Road, Loughrea | €220,000 | 13 |
| Old Mill Rd, Poolboy | €310,000 | 9 |
| Olde Meadows, Portnick | €331,938 | 8 |
| Oldfield, Kingston | €484,500 | 14 |
| Oran Close, Oranhill | €339,207 | 16 |
| Oran Crescent, Oranhill | — | 9 |
| Oran Island, Oranmore | — | 12 |
| Oranbay, Oranhill | — | 7 |
| Oranbay Apts, Oranhill | €254,500 | 10 |
| Oranbeg, Oranmore | — | 7 |
| Oranclose, Oranhill | — | 7 |
| Orancourt, Oranhill | — | 5 |
| Oranglen, Oranhill | — | 7 |
| Orangreen, Oranhill | — | 7 |
| Orangrove, Oranhill | — | 12 |
| Oranhill, Oranmore | — | 5 |
| Oranhill Avenue, Oranmore | — | 7 |
| Oranhill Road, Oranhill | — | 14 |
| Oranisland, Oranmore | — | 5 |
| Oranswell, Bushypark | — | 5 |
| Oranview, Oranhill | €375,000 | 12 |
| Ower, Headford | €25,000 | 13 |
| The Orchard, Gort | — | 10 |
| The Orchard, Kingston | — | 8 |
| The Orchard, Moylough | €185,000 | 41 |