I read a throwaway article today that claimed that celebration of St. Patrick's Day was originated by Irish immigrants to America. Dubious of this fact, I did a search on the history of the holiday and only found facts about St. Patrick himself, not the history of the festival. I did read that until the 1970s, pubs in Ireland were closed on this day as it was a religious holiday - which would suggest that the holiday had been celebrated prior to US immigration.
Can anyone shed light? How involved were Irish-Americans in making this holiday as well-celebrated as it is today?
It depends on what you mean by 'celebrated'.
The feast day of the death of St Patrick - recorded in the ancient Irish annals as 17th March - has been a day of commemoration and a Christian feast day in Ireland since the 8th century. Some sources credit it with starting with the Irish missionaries abroad on the European continent during that time but within Ireland Patrick was an important figure in Irish Christianity and especially for the Uí Néill dynasty, who claimed Patrick as their patron. It was the scribes of the Uí Néill who, in the 7th century, created the many myths surrounding Patrick. Stories of confronting druids, lighting fires to chase pagan gods etc. are all created stories. They also essentially invented the notion of him being the first and sole convertor of the Irish to Christianity. This was a way of bolstering the importance of the Uí Néill who claimed Patrick had founded their church and monastery at Armagh. There is no evidence that Patrick was ever even in Armagh. Nevertheless Patrick's cult survived and he became the great champion of Irish Christianity.
The feast day has been a holy day in Ireland going back over 1,000 years. The shamrock myth - and the wearing of the shamrock on that day - was introduced during the 16th century.
The American style celebration - associated with large parades and alcohol- was not the way it was celebrated in Ireland until the late 1970s. In Ireland the pubs traditionally closed because it was a holy day. The Dublin parade was a low key affair showcasing local Irish businesses. With tourism it is true to say that the day became more Americanised in Ireland. But this is just another twist in the history of the feast of St Patrick.