The Washoe County Courthouse was DeLongchamps's first major commission. In 1909 the county selected his plans in a competition, giving him a distinction that initiated a remarkable career. DeLongchamps went on to design six more county courthouses in Nevada, each stylistically indebted to Beaux-Arts classicism, although they show a steady move toward simplicity that culminates in the elegant lines of the Pershing County Courthouse.
The courthouse in Reno has clearly articulated components, strong Corinthian columns, and an ornate entablature. A sweeping staircase leads to the two-story Corinthian portico and a pair of paneled metal doors. Wide Doric pilasters flank windows with terra-cotta surrounds including bracketed pediments on the first floor and square moldings with keystones on the second. A large copper ribbed dome, rising from a stone drum embellished by pedimented dormers, crowns the building. Inside, DeLongchamps called for ornate metal balustrades, gray marble wainscot, pilasters with black marble bases, and multicolored tile floors. The ceiling of the second-floor hallway has a shallow dome of colored, leaded glass that reveals the light from the dome above.
DeLongchamps's ability to create appealing buildings kept his practice active until his retirement in 1965, and the long span of his career gave him the unusual opportunity to add to buildings he had designed decades earlier. In the 1940s his firm designed matching wings for the courthouse and, in 1963, an addition to the rear in a modernist style that contrasts dramatically with the early twentieth-century building.