Louis A. Simon (1867–1958) was an American architect. He was born in Baltimore, Maryland.
Simon was educated at the Massachusetts Institute of Technology. Following a tour of Europe, he opened an architectural office in Baltimore, Maryland in 1894.
Simon served as Supervising Architect in the Office of the Supervising Architect, U.S. Department of the Treasury from 1933 until 1939, when the office was moved to the Public Works Administration / Works Progress Administration. He had been associated with the office from 1896; Edward A. Crane, Superintendent of Architects in the office between 1905 and 1933, originally recruited Simon to the office.
From 1915 to 1933, during the tenure of Acting Supervising Architect James A. Wetmore, a lawyer and a political appointee, Simon was responsible for the direction of much of the design work. Most of Simon's buildings, notably post office buildings, were designed in the Colonial Revival style. Occasionally, buildings were designed in a restrained or more stylized classically derived style. Simon was unwavering in his defense of what he considered a "conservative-progressive" approach to design in which he saw "art, beauty, symmetry, harmony and rhythm".