Slidell, LA has a population of 27,697 and is the 1,548th largest city in the United States. The population density is 1,808 per sq mi which is 1938% higher than the Louisiana average and 1895% higher than the national average. The median age in Slidell is 38 which is approximately 6% higher than the Louisiana average of 36. In Slidell, 55% of the population over 15 years of age are married, 92% speak English and 5% speak Spanish. 65% of Slidell residents were born in Louisiana, 30% were born out of state, 1% were born outside of the United States and 4% were foreign born.