A sundown town is a town that is or was purposely all-white. The term is widely used in the United States in areas from Ohio to Oregon and well into the South. The term came from signs that were allegedly posted stating that people of color had to leave the town by sundown.  The minority people could not visit after sunset or spend the night in the town (even as a paying hotel customer). Such towns are also sometimes called “sunset towns” or “gray towns”.

History
Some towns placed signs at the town's boundary with statements similar to the one posted in Hawthorne, California, which read "Nigger, Don't Let The Sun Set On YOU In Hawthorne" in the 1930s.

In some cases, keeping minorities out was official town policy, through restrictive covenants written in land deeds, or by agreement between the real estate agents of the community. In others, the policy was enforced through intimidation. For example, law enforcement officers could stop all minorities found after sunset.

Though no one knows the number of sundown towns in the United States, the largest estimate was that the nation had several thousand. The highest proportion of confirmed sundown towns are in the state of Illinois. It is difficult to confirm sunset towns because the towns did not keep, or do not want to show, official documents stating their status as sundown towns. For example, One Hundred Years of Progress: The Centennial History of Anna, Illinois, although more than 400 pages long, never mentions Anna's 1909 expulsion of African Americans, the sundown signs at the northern and southern city limits in 1954, or anything else about race. 

Since the civil rights movement of the 1950s and 1960s, and especially since the Civil Rights Act of 1968 prohibited racial discrimination concerning the sale, rental, and financing of housing, the number of sundown towns has decreased. However, as sociologist James Loewen writes in his book on the subject, it is impossible to precisely count the number of sundown towns at any given time, because most towns have not kept records of the ordinances or signs that marked the town's sundown status. His book, Sundown Towns: A Hidden Dimension of American Racism, notes that hundreds of cities across America have been sundown towns at some point in their history.

Loewen's book mentions that sundown status meant more than just African-Americans not being able to live in these towns. Essentially any African-Americans (or sometimes other groups) who came into sundown towns after sundown were subject to harassment, threats, and violent acts—up to and including lynching.

Other minorities targeted
In addition to the expulsion of African Americans from some small towns, Chinese Americans and other minorities were also driven out of some of the towns where they lived. Loewen says one example is that in 1870, Chinese made up one-third of the population of Idaho. Following a wave of violence and an 1886 anti-Chinese convention in Boise, almost none remained by 1910. The town of Gardnerville, Nevada, is said to have blown a whistle at 6 p.m. daily alerting Native Americans to leave by sundown.
In addition, Jews were excluded from living in some sundown towns, such as Darien, Connecticut.

Books that refer to Sundown towns 
James Loewen's book, Sundown Towns describes sundown towns.  Several other books also show the existence of sundown towns.  Sundown towns are mentioned in Following the Color Line, by Ray Stannard Baker; Free But Not Equal, by V. Jacque Voegeli; Black Ohio and the Color Line, by David Gerber; The Negro in Indiana, by Emma Thornbrough; Mobile Americans: Residential and Social Mobility in Omaha, by Howard Chudacoff; Race and Kinship in a Midwestern Town, by James DeVries; The Sociogenesis of a Race Riot by Roberta Senechal.  Visual treatments include Robby Heason, Trouble Behind (Cicada Films, 1990), and Marco Williams, Banished (banishedthefilm.com/).

References

Further reading

Other websites
 Encyclopedia of Arkansas History & Culture entry: Sundown Towns
 Review and feature article, Dallas Morning News 
 Interview with James Loewen, U.S. News
 Article on Vidor, Texas's long time reputation as a sundown town

American civil rights