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.
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.