In the 9th and 10th centuries, Saint Patrick's day was being celebrated widely throughout Ireland. By the Medieval period, Patrick became the undisputed Patron Saint of Ireland. By the 17th century, green had increasingly been associated with Ireland. As the color became associated with the country and people, naturally Saint Patrick, the patron saint, began to also be associated with this color, leading to this color being the primary color worn on the feast day. In the 17th century, Luke Wadding, an important Franciscan friar from Ireland, placed Saint Patrick as part of the official important feast days in the Catholic calendar. The Vatican recognized Saint Patrick's day in 1631 as a feast day.<ref>For more on the development of Saint Patrick as the Patron Saint of Ireland, see: Duffy, S., MacShamhráin, A., & Moynes, J. (Eds.). (2005). <i>Medieval Ireland: an encyclopedia</i>. New York: Routledge, pg. 66.</ref>
Even after the conversion and migration of English to Ireland in the 1600s, the Anglican calendar has retained Saint Patrick as part of their celebrations. In the 19th and 20th centuries, Saint Patrick's day began to take a nationalistic characteristic against Protestant and British forces in Ireland. In 1903, Saint Patrick's day in Ireland held its first parade in Waterford, which was the home of the bishop who had created Saint Patrick's day as an official feast day. In 1916, large-scale Saint Patrick's day marches and parades were held in Ireland, where the Irish Volunteers sponsored these marches and parades. Some accounts suggest many or even most of the participants may have been armed, signifying the troubled period during British occupation throughout Ireland. With the partition of Ireland after the creation of the Irish Free State, celebrations in Northern Ireland began to reflect Protestant and Catholic divisions. The Unionists of Northern Ireland, although recognizing Saint Patrick's day as a holiday, did not hold any official celebrations, while the Catholics used the day as a way to protest against the Unionists.
In the United States, widespread migration in the 19th century led to celebrations of Saint Patrick's day
already in the mid-19th century. However, it has been claimed that already by 1762 celebrations of Saint Patrick's day, and even the first official parade, had taken place. It is then possible or even likely that the first Saint Patrick's parade took place in New York. In the mid-19th century, widespread celebrations and parades were held in places such as New York and Boston. US traditions, in may respects, in the 20th century influence the global spread and influence of Saint Patrick's day.