Newcastle was founded in the 19th century. According to Transcontinental Railroad Landmarks the "Regular freight and passenger trains began operating over the first 31 miles of Central Pacific's line to Newcastle June 10, 1864, when political opposition and lack of money stopped further construction during that mild winter. Construction was resumed in April, 1865." The region is also in the vicinity of what was the cradle of "gold country", where in the mid-19th century a flurry of miners and gold prospectors searched for their fortune. During this time however, the town of Newcastle was known more for its orchards rather than abundant gold mines. The Newcastle post office opened in 1864.
The 2010 United States Census reported that Newcastle had a population of 1,224. The population density was 510.8 people per square mile. The racial makeup of Newcastle was 1,113 White, 104 Hispanic or Latino of any race, 19 Native American, 17 Asian, 7 African American, 35 from other races, and 33 were from two or more races. The Census reported that 1,216 people lived in households, 8 lived in non-institutionalized group quarters, and 0 were institutionalized. There were 545 households, out of which 115 had children under the age of 18 living in them, 258 were opposite-sex married couplesliving together, 42 had a female householder with no husband present, 23 had a male householder with no wife present. There were 25 unmarried opposite-sex partnerships, and 2 same-sex married couples or partnerships. 186 households were made up of individuals and 117 had someone living alone who was 65 years of age or older. The average household size was 2.23. There were 323 families ; the average family size was 2.86. The population was spread out with 220 people under the age of 18, 83 people aged 18 to 24, 191 people aged 25 to 44, 416 people aged 45 to 64, and 314 people who were 65 years of age or older. The median age was 51.3 years. For every 100 females, there were 91.3 males. For every 100 females age 18 and over, there were 92.3 males. There were 597 housing units at an average density of 249.1 per square mile, of which 430 were owner-occupied, and 115 were occupied by renters. The homeowner vacancy rate was 4.4%; the rental vacancy rate was 12.2%. 923 people lived in owner-occupied housing units and 293 people lived in rental housing units.
