O'Neill, county seat of Holt County, was founded by General John O'Neill, a native of Ireland and veteran of the American Civil War. The "general," a rank bestowed on him by admirers because he commanded three Fenian incursions into British-governed Canada, first directed colonists in 1874 to this fertile Elkhorn Valley site which bears his name. General O'Neill also induced other Irish groups to settle at Atkinson in Holt County and in Greeley County.

Many Irish coming to O'Neill had emigrated to America earlier, as result of famine and economic distress, temporarily settling in eastern cities. General O'Neill, knowing the agricultural heritage of his people, said his object in founding Nebraska colonies was "to encourage poor people in getting away from the overcrowded cities of the East."

The Irish were a major immigrant group contributing to the settlement of Nebraska. Speaking the English language, they blended into the population and were found in many communities. However, due to ancient animosities with Britain, some of them colonized in America. Foremost colony in this state is O'Neill, proclaimed the Irish Capital of Nebraska by the Governor in 1969.