BALLINA, Ireland — In this removed County Mayo town at the mouth of the River Moy, the widow of a local fish merchant decided one day to share her husband’s collection of Irish miscellany with the public. Better to have it on display here in his beloved Ballina, as he had always wished, than to lose it, God forbid, in a fire in the family home above the family shop, Clarke’s Salmon Smokery.

The six-week job of selecting the best items for an exhibition fell to Sinead McCoole, an author and historian who came the 150 miles from Dublin. She knew that this curious fish man, Jackie Clarke, was said to have acquired a rare, original copy of the 1916 Easter Proclamation — Ireland’s Declaration of Independence — but local collections rarely warrant the enthusiasm of their owners. Her expectations remained at low tide.

Ms. McCoole made her way down the town’s ancient commercial row to the home above the shop, where the sight of some old but unremarkable books left her wondering whether six weeks in Ballina would be a few weeks too long. But then the widow, Anne Clarke, led the skeptical scholar to her husband’s “locked room,” for many years off limits even to family. Inside were bundles and bundles wrapped in parcel paper; fish boxes and fish boxes packed with documents; stuff, and stuff, and more stuff.

Six weeks became six months, and then a year, and then — well, Ms. McCoole is still in Ballina nearly eight years later, still immersed in what is now known as the Jackie Clarke Collection: an astounding treasure of more than 100,000 items that provide an intimate retelling of Ireland’s long struggle to free itself of English rule. Fragile maps and rare newspapers, political posters and editorial cartoons, books, diaries, photographs, films, and even a scrapbook that Clarke began as a boy.