Origins of term
Red-light districts are mentioned in the 1882 minutes of a Woman's Christian Temperance Union meeting in the United States. The Oxford English Dictionary records the earliest known appearance of the term "red light district" in print as an 1894 article from the Sandusky Register, a newspaper in Sandusky, Ohio
Author Paul Wellman suggests that this and other terms associated with the American Old West originated in Dodge City, Kansas, home to a well-known prostitution district during the 19th century, which included the Red Light House saloon. This has not been proven, but the Dodge City use was likely responsible for the term becoming pervasive. A widespread folk etymology claims that early railroad workers took red lanterns with them when they visited brothels so their crew could find them in the event of an emergency. However, folklorist Barbara Mikkelson regards this as unfounded.
One of the many terms used for a red-light district in Japanese is akasen (赤線), literally meaning "red-line". (This has independent origins from the same term in English.) Japanese police drew a red line on maps to indicate the boundaries of legal red-light districts. In Japanese, the term aosen (青線), literally meaning "blue-line", also exists, indicating an illegal district.
In the United States during the 19th and early 20th centuries, the term "sporting district" became popular for legal red-light districts. Municipal governments typically defined such districts explicitly to contain and regulate prostitution.