First found in county Kildare, seated at O'Toole's Castle, where they were descended from Tuathal, King of Leinster who died in 950 A.D.

Death and immigration greatly reduced Ireland's population in the 19th century. For the native Irish people poverty, hunger, and racial prejudice was common. Therefore, thousands left their homeland to seek opportunity in North America. Those who survived the journey and the quarantine camps to which they arrived, were instrumental towards building the strong developing nations of the United States and the future Canada. By far, the largest influx of Irish settlers occurred with Great Potato Famine during the late 1840s. These were employed as construction or factory workers. An examination of passenger and immigration lists has shown early immigrants bearing the name O'Toole: Ann Tool arrived in America in 1702; Christian Tool settled in Virginia in 1726; John Tool settled in Maryland in 1775; followed by Robert in 1776; James Tool settled in Boston Mass in 1766.

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