Oldwick is an unincorporated community located within Tewksbury Township in Hunterdon County, New Jersey, United States. The area is served as United States Postal Service ZIP Code 08858. As of the 2000 United States Census, the population for ZIP Code Tabulation Area 08858 was 177. The 2010 census data indicate a population of 144, comprising 68 housing units. Oldwick is the corporate headquarters of the A. M. Best rating agency, and is the location of Mane Stream, formerly the Somerset Hills Handicapped Riding Center for adaptive riding and equine assisted therapy.