North Castle is a town in Westchester County, New York, United States. The population was 11,841 at the 2010 census, it has three hamlets: Armonk and North White Plains. According to the United States Census Bureau, the town has a total area of 26.5 square miles, of which 24.1 square miles is land and 2.4 square miles, or 9.06%, is water. As of the census of 2000, there were 10,849 people, 3,583 households, 3,002 families residing in the town; the population density was 450.4 people per square mile. There were 3,706 housing units at an average density of 153.9 per square mile. The racial makeup of the town was 92.38% White, 1.76% African American, 0.03% Native American, 3.96% Asian, 0.05% Pacific Islander, 0.63% from other races, 1.20% from two or more races. Hispanic or Latino of any race were 4.14% of the population. There were 3,583 households out of which 44.2% had children under the age of 18 living with them, 74.6% were married couples living together, 6.9% had a female householder with no husband present, 16.2% were non-families.

13.1% of all households were made up of individuals and 5.5% had someone living alone, 65 years of age or older. The average household size was 2.99 and the average family size was 3.28. In the town, the population was spread out with 29.7% under the age of 18, 4.5% from 18 to 24, 26.8% from 25 to 44, 28.3% from 45 to 64, 10.7% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 97.1 males. For every 100 females age 18 and over, there were 94.7 males. The median income for a household in the town was $117,815, the median income for a family was $141,764. Males had a median income of $86,950 versus $49,500 for females; the per capita income for the town was $60,628. About 1.0% of families and 3.0% of the population were below the poverty line, including 1.7% of those under age 18 and 3.4% of those age 65 or over. North Castle has each taking the form of a hamlet. Armonk – a hamlet located in the central part of the town, it is the seat of the main town library.

Banksville – a hamlet known as the "Eastern District of North Castle", located in the eastern part of the town, close to Connecticut. North White Plains – a hamlet located in the southern part of the town, it is south of the Kensico Reservoir Dam, west of the White Plains Reservoirs, east of the Bronx River, although the name refers to any portion of North Castle south of the Kensico Reservoir. The Elijah Miller House was added to the National Register of Historic Places in 1976. Due to its proximity to Manhattan and its idyllic setting, a number of major companies call Armonk home. IBM has its world headquarters in Armonk, its principal building, referred to as CHQ, is a 283,000-square-foot glass and stone edifice on a 25-acre parcel amid a 432-acre former apple orchard the company purchased in the mid-1950s. The American headquarters of Swiss Re is located in Armonk on a 127-acre site overlooking the Kensico Reservoir. In addition M. E. Sharpe, the academic publisher has its headquarters in Armonk.

According to North Castle's 2011 Comprehensive Annual Financial Report, the top employers in the city are: Supervisor - 2009 William Weaver - 1,648 - 46% Frank Benish - 990 - 27% Becky Kittredge - 965 - 27%Councilman - 2009 John J. Cronin - 2,311 - 35% Diane Roth - 1,800 - 27% Bob Romano - 1,437 - 22% Stacey Slipe - 1,118 - 17%Supervisor - 2005 John Lombardi - 1,901 - 43% Reese Berman - 2,264 - 51% Anthony Futia, Jr. - 233 - 5%Councilman - 2005 William Weaver - 2,089 - 26% John Stipo - 1,398 - 18% Anthony Baratta - 1,953 - 24% Gerry Geist - 2,548 - 32%Supervisor - 2001 John Lombardi - 2,950 - 100%Supervisor - 1999 John Lombardi - 1,562 - 100%Supervisor - 1997 John Lombardi - 2,827 - 100%Supervisor - 1989 John Lombardi - 2,126 - 74.21% John Stipo - 739 - 25.79% 1800 – 1,168 1850 – 2,189 1900 – 1,471 1950 – 3,855 2000 – 10,849 2010 – 11,841Population growth in North Castle reflects the pattern of rural to suburban development typical of the post-World War II years. Like many other suburban communities in Westchester County and the nation, the town experienced a surge of population growth between 1940 and 1970.

The overall rate of growth was moderate between 1970 and 1990 because of national economic conditions, including the rising cost of land and interest, which helped to bring about a general decline in housing construction. The median price of houses sold in North Castle in 1998 was $600,000. Town of North Castle official website

The principal tributaries of the Colorado River of North America are the Gila River, the San Juan River, the Green River, the Gunnison River. The following is a tree demonstrating the points at which the major and minor tributaries of the Colorado River branch off from the main river and from each other. Fraser River Muddy Creek Blue River Snake River Tenmile Creek Eagle River Gore Creek Roaring Fork River Fryingpan River Crystal River Plateau Creek Gunnison River East River Slate River Taylor River Tomichi Creek Cochetopa Creek Quartz Creek Lake Fork Gunnison River Henson Creek Uncompahgre River Smith Fork North Fork Gunnison River Little Dolores River Dolores River West Dolores River San Miguel River Green River Big Sandy River Blacks Fork Henry's Fork Sheep Creek Carter Creek Cart Creek Crouse Creek Vermillion Creek Yampa River Elk River Little Snake River Jones Hole Creek Duchesne River White River Willow River Price River White River Range Creek San Rafael River Dark Canyon Dirty Devil River Muddy Creek Fremont River Escalante River San Juan River East Fork San Juan River West Fork San Juan River Wolf Creek Navajo River Piedra River Los Pinos River Animas River Florida River La Plata River Chaco River Mancos River Chinle Creek Paria River Little Colorado River Zuni River Rio Nutria, tributary to the Zuni River Rio Pescado, tributary to the Zuni River Puerco River Bright Angel Creek Tapeats Creek Thunder River Deer Creek Kanab Creek Havasu Creek Diamond Creek Virgin River Meadow Valley Wash Muddy River Las Vegas Wash Bill Williams River Santa Maria River Big Sandy River Gila River San Francisco River Tularosa River San Pedro River Santa Cruz River Salt River Black River Tonto Creek Verde River Oak Creek Agua Fria River Hassayampa River Hardy River Gulf of California- Grand Canyon Rapids and Features River and Tributary Locations determined by examining maps available at USGS national atlas