O'Neill
- County:
- Holt County
- County Seat:
- Yes
- Area (mi²):
- 2.339
- State:
- Nebraska
O'Neill is a city located in Holt County, Nebraska. O'Neill has a 2026 population of 3,578. It is also the county seat of Holt County. O'Neill is currently declining at a rate of -0.45% annually but its population has increased by 0.2% since the most recent census, which recorded a population of 3,571 in 2020.