() is a city situated on the northeast shore of Lake Pontchartrain in St. Tammany Parish, Louisiana, United States. The population was 25,695 at the 2000 census. The Greater Slidell Community has a population of about 90,000. It is part of the New Orleans–Metairie–Kenner Metropolitan Statistical Area.
Slidell is located at (30.279040, -89.777744) and has an elevation of . It is at the southeastern tip of St. Tammany Parish in Louisiana's Ozone Belt and is approximately three miles from the north shore of Lake Pontchartrain.
According to the United States Census Bureau, the city has a total area of 12.1 square miles (31.4 km²), of which, 11.8 square miles (30.5 km²) of it is land and 0.3 square miles (0.8 km²) of it (2.64%) is water.