| O'Brien | |
| Official Name: | Former Town of O'Brien |
| Native Name Lang: | zh-cn |
| Pushpin Map: | Ontario |
| Pushpin Map Caption: | Location in Ontario |
| Pushpin Label Position: | bottom |
| Pushpin Label: | O'Brien |
| Coordinates: | 47.6742°N -80.7433°W |
| Subdivision Type: | Country |
| Subdivision Name: | Canada |
| Subdivision Type1: | Province |
| Subdivision Name1: | Ontario |
| Subdivision Type2: | District |
| Subdivision Name2: | Timiskaming District |
| Subdivision Type3: | Township |
| Subdivision Name3: | Nicol Township |
| Subdivision Type4: | Village-level divisions |
| Unit Pref: | Metric |
| Population Density Km2: | auto |
| Postal Code Type: | Postal code |
| Postal Code: | POJ 1J0 |
O'Brien is a former mining town in northeastern Ontario near Gowganda with a warm-summer humid continental (Dfb) Köppen climate classification. The mining town serviced several mines including silver mines around nearby lake Miller Lake; one of the past-producing silver mines was Ontario's largest producing Cobalt-style silver mine outside of Cobalt, with historical production of 40.7 million ounces of silver between 1910 and 1972.[1] [2]