John and Ellen O’Neil (nee Dougherty) arrived in the United States from Ireland in 1871, and joined the Clemens household when John was hired as the gardener in 1885. He earned $50 a month, and later $60, but did not receive room and board as some servants did. To supplement their income, they sold flowers from the greenhouse on the property, switching to Christmas trees at the proper time of year. Samuel Clemens wrote that the O’Neils were two of “the three persons I have had long acquaintance with who could be trusted to do their work well & faithfully without supervision,” the third being coachman Patrick McAleer.

When financial troubles led the Clemenses to close up the house and leave for Europe in 1891, the O’Neils moved into the house and served as caretakers. Olivia Clemens wrote to Ellen O’Neil in 1892: “I am sure everything is going well and I do not have one single moment of worry about anything there. I know that you and John will take good care of everything.” When the Clemens rented the house for a period, the O’Neils moved into the second floor of the carriage house, where McAleer and his family had once resided, and took care of the property until it was sold in 1903. Photographs of the house during this period clearly show their advertising sign on the lawn: It reads “CUT FLOWERS FOR SALE \ JOHN O’NEIL.”

When Olivia Clemens died in Italy in 1904, the O’Neils wrote a letter of condolence and sent flowers. Samuel Clemens answered: Of all the tributes of homage & affection for our lost one that have come from her friends in many lands, that which came from you & John has moved me most & touched me deepest. Those white roses spoke a message of love as pure & fragrant as themselves; & the like of that love was in Mrs. Clemens’s heart for you two to her last day. She held you in as high honor as she held any of her other friends, & she never spoke your names but with affection.