First found in county Down, where they held a family seat from ancient times.

Ireland, as an English-controlled colony in the 19th century, suffered the loss of hundreds of thousands of its native people. The system of land ownership often did not sufficiently provide for the tenants who farmed the land. This was most clearly evidenced in the Great Potato Famine of the 1840s. Previous years of great demand for grain products and livestock had run the land down. Many landowners foreseeing an upcoming crisis often removed families from the land or forced them to rely on pityfully small plots where only a subsistence living could be made. When the famines of 1845, 46, and 48 hit, many had nothing. Disease and starvation became widespread and families boarded ships for elsewhere any way they could. Those who went to America were instrumental in developing the industrial power known today: many Irish were employed in hard labor positions in factories and in building the bridges, canals, roads, and railways necessary for a strong industrial nation. Research of early immigration and passenger lists has shown that many bearers of the name McGinnis: John Guinnessy, who settled in New York in 1849; William Guinnes who settled in the Barbados in 1663; Pat and Mary Guinnessy who settled in Quebec with their ten children in 1849.

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