Sinclair, Wyoming, first known as Parco, is ''truly an oasis in an otherwise drab desert territory,'' reported the Rocky Mountain News in August of 1925. The town of Sinclair was a company-built town designed by the Denver-based architectural firm of Fisher and Fisher. It was financed by oil magnate Frank Kistler to house workers for a large Producers and Refiners Oil Company refinery built in 1922-1923 at this location. Sinclair was constructed in 1924-1925 and consists of numerous public buildings set around three sides of a central east-west plaza, fountain and park. Residences are located along streets and blocks in a grid pattern running north, west and east from the plaza area.

In order to foster a sense of community spirit commonly absent in company towns, as well as to maintain an architectural cohesiveness, the architects designed residential and public buildings using Spanish Colonial motifs with unpainted stucco, polychrome clay tile roofs, and dominant masonry construction to accurately simulate the appearance and form of many southwestern adobe missions. There are a total of ninety three buildings included within the district boundaries, forty nine of which are contributing elements of the district.

The most prominent public building is the impressive Parco Inn which dominates the plaza and establishes the overall architectural theme. Although Kistler's firm was forced to sell the PARCO holdings in 1934 when crude oil reached an all-time low price of ten cents a barrel, the oil market improved as a result of increased demand during World War II. The refinery and town, renamed Sinclair in 1942, prospered under the management of the Sinclair Refining Company. From its inception, Sinclair remained one of the most important refineries in the State of Wyoming.