His design of the second Vermont State House brought him fame and success, which eventually led him to become the first Supervising Architect of the U.S. Treasury Department.

As federal architect, he was responsible for creating across the United States numerous custom houses, post offices, courthouses and hospitals, many of which are today on the National Register.

Indeed, his design for the Federal style First Congregational Church, built in Lebanon in 1828, borrows significantly from Plate K of The American Builder's Companion.

His first monumental work was the Second Vermont State House, a cruciform Greek Revival structure built between 1833 and 1838, which combined a Doric portico modeled on the Temple of Theseus in Athens, with a low saucer dome inspired by the Pantheon in Rome.

Entering the 1837 competition to design the Boston Custom House, Young submitted another cruciform scheme combining a Greek Doric portico with a Roman dome.

Mandated to be fire-proof, the custom houses, post offices, courthouses and hospitals he built featured masonry foundations, walls and vaulting, with cast iron interior structural and decorative elements, including columns, stairways and railings.

Column capitols, fascia and pediments on the exterior, when not stone, were cast iron painted to look like stone—which drew criticism of parsimony by the federal architect.

At the same time, ongoing modifications to the Treasury Building concerned Young, expected to create working drawings based on plans by Walter.

For the South Wing, he invented a column capital which symbolized the department, substituting acanthus leaves of the Corinthian order with eagles and a fist holding a key.