Oldwick is an unincorporated community and census-designated place (CDP) located within Tewksbury Township in Hunterdon County, in the U.S. state of New Jersey. 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.