Zachary, LA has a population of 16,154 and is the 2,653rd largest city in the United States. The population density is 635 per sq mi which is 616% higher than the Louisiana average and 601% higher than the national average. The median age in Zachary is 34 which is approximately 5% lower than the Louisiana average of 36. In Zachary, 58% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 80% of Zachary residents were born in Louisiana, 19% were born out of state, 0% were born outside of the United States and 1% were foreign born.