Water Mill, NY has a population of 2,349 and is the 10,160th largest city in the United States. The population density is 223 per sq mi which is 38% lower than the New York average and 146% higher than the national average. The median age in Water Mill is 55 which is approximately 43% higher than the New York average of 38. In Water Mill, 69% of the population over 15 years of age are married, 81% speak English and 11% speak Spanish. 66% of Water Mill residents were born in New York, 14% were born out of state, 0% were born outside of the United States and 21% were foreign born.