The construction of Florham between 1893 and 1899 brought together an extraordinary concentration of talent. McKim, Mead & White modeled the design loosely on Hampton Court Palace. Frederick Law Olmsted, who had designed Central Park and the grounds of Biltmore, laid out the Italianate gardens that survive today; standing at the site, he told Twombly that the view was 'as much so as if you owned the state of New Jersey.' Thomas Edison — who had received early financial support from Twombly and J.P. Morgan — personally designed the mansion's heating system and boiler, installed in a tunnel system beneath the house. The resulting estate included vast greenhouses, an orangery, a dairy farm, stables, a gatehouse, and a carriage house, all set on grounds that Olmsted managed with the same attention he gave to public parks.

Hamilton McKown Twombly died in 1910. Florence survived him by 42 years, maintaining the estate's lavish Gilded Age scale long after most such households had contracted. She died in 1952, and her daughter Ruth died two years later. By then, the Vanderbilt fortune could no longer sustain Florham's lifestyle, and the estate was broken up and sold in 1955. None of the Vanderbilt estates survived in family hands, except Biltmore in North Carolina. Arthur T. Vanderbilt II observed with a certain melancholy that these mansions had been 'built for eternity' but were 'hardly used for a lifetime' and 'none was occupied by the next generation.' Several months before the auction, William Burden, son of Florence Twombly Burden, donated dozens of the mansion's interior fittings to the White House. Several chairs from Florham have sat in the Oval Office under Presidents George W. Bush, Barack Obama, and Donald Trump.

In 1958, the mansion and 187 acres of grounds were sold to Fairleigh Dickinson University for use as a Morris County campus. The carriage house became science labs. The orangery — the glass greenhouse structure that Florence Vanderbilt had used to grow citrus — was preserved and now functions as the reading room of the campus library. The founding university president, Peter Sammartino, oversaw the hasty renovation and opened the campus to students in the fall of 1958. Students now write papers and take exams in rooms where the Vanderbilts once entertained industrialists and dignitaries. The mansion remains one of the ten largest houses in the United States, though its corridors now carry backpacks rather than the rustle of Gilded Age dress. In 1990, the Friends of Florham was founded to support the mansion's gradual restoration — a recognition that keeping something this large and this old requires ongoing commitment, not just an initial purchase.

Walking the grounds of Florham today, the Olmsted gardens are the most immediate evidence of the original vision. Formal in structure, Italian in reference, they were designed to feel inevitable — as if the landscape had always been this way, the trees and hedges arranged by nature rather than by the most celebrated landscape architect in American history. The mansion itself presents a Georgian Revival facade that reads, from the approach, more like an institution than a home. That has become its truth. Tiffany stained-glass windows memorializing Alice Twombly — a daughter who died in 1896 at age sixteen — can still be seen at Grace Church in Madison, a few miles from the campus. The estate that was 'built for eternity' did not stay a Vanderbilt possession, but it did endure.