Rikers Island is located in the Long Island Sound (actually the East River, but it's close), approximately midway between Queens and The Bronx. It is legally a part of Bronx County, although the only way to reach it is via a bridge from Queens.

It was, in fact, originally a part of Queens, becoming a part of the Bronx in 1914.

The island was bought from the Riker family in 1884 for $180,000. The island, then only 87 acres, was previously used as training ground for New York's 20th and 26th regiments of the "United States Colored Troops" during the Civil War. It was also used as a military base and barracks during the same war, garnering complaints due to its being a summer facility used in the winter.

From 1893 on, the island was used as a dump, not only for the general garbage of the city, but also for the dirt removed from the ground during the digging of the subway. This trash and landfill caused the island to grow in size to its present 415 acres.

Rikers Island is best known for, and synonymous with, the jail located there. The prison was originally located on Roosevelt Island (then known as Welfare Island), and was moved to Rikers in 1935.

The New York City Department Of Corrections maintains its headquarters there. Along with the 10 jails that make up the complex, the Department’s Transportation Division, central laundry, central bakery, K-9 and Marine units can also be found there.

General Facts: (all stats 1999 unless otherwise noted)

Admissions: 127,029
Average Daily Population: 17,562
%of Capacity: 98.5%
Average Annual Cost Per Inmate: $47,083


References:

http://www.correctionhistory.org/html/chronicl/cw_units/html/cwriltrs.html
http://www.correctionhistory.org/html/chronicl/nycdoc/html/usct01.html
http://www.ci.nyc.ny.us/html/doc/html/history.html
http://www.villagevoice.com/issues/0050/gonnerman1.shtml
http://www.newsday.com/liname/nynam70.pdf