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Where is the O'sullivan family from?
You can see how O'sullivan families moved over time by selecting different census years. The O'sullivan family name was found in the USA, the UK, Canada, and Scotland between 1861 and 1920. The most O'sullivan families were found in USA in 1880. In 1880 there were 332 O'sullivan families living in New York. This was about 32% of all the recorded O'sullivan's in USA. New York had the highest population of O'sullivan families in 1880.
Use census records and voter lists to see where families with the O'sullivan surname lived. Within census records, you can often find information like name of household members, ages, birthplaces, residences, and occupations.