thumb|St. Tammany Parish Justice Center in Covington

thumb|[[Madisonville, Louisiana|Madisonville's Tchefuncte River Lighthouse stands on the Saint Tammany Northshore of Lake Pontchartrain. This lighthouse was built in 1837.]]

St. Tammany Parish (; ) is a parish located in the U.S. state of Louisiana named after Tamanend, the legendary Lenape Chief of Chiefs and the "Patron Saint of America." At the 2020 census, the population was 264,570, making it the fourth-most populous parish in Louisiana. The parish seat is Covington. The parish was founded in 1810.

St. Tammany Parish comprises the Slidell–Mandeville–Covington metropolitan statistical area, which is also included in the New Orleans–Metairie–Slidell combined statistical area. St. Tammany Parish is one of the fastest-growing parishes in the state, along with Livingston and Ascension. The population has quadrupled since 1970, and is expected to double again by 2030, expecting to diversify the population of the parish. Though it was not heavily directly damaged by Hurricane Katrina, the community is growing in large part due to subsequent displacement of populations, with many coming from the New Orleans metropolitan area seeking to avoid hurricane and weather-related threats, caused in part due to climate change. Among the nine Louisiana parishes named after saints, St. Tammany is the only one whose eponym is not a saint of the Catholic Church, the ecclesiastical parishes of which had formed the basis for the state's civil parishes. Tamanend is not known to have been Roman Catholic or Christian, but he had been popularly revered as a "Patron Saint of America" since the post-Revolutionary period, long after his death.

19th century

In the early 1830s, there were only two towns in St. Tammany: Covington, a retreat with summer homes and hotels; and Madisonville, a shipbuilding and sawmill town. The area south of Covington to Lake Pontchartrain's northern shore and extending eastwards to the Pearl River border with the state of Mississippi was known as the Covington Lowlands. This region included the present-day towns of Mandeville, Abita Springs, Lacombe, Slidell, and Pearl River.

Mandeville was founded in 1834 by Bernard de Marigny de Mandeville and was developed as a health resort for wealthy New Orleanians, because it was believed that ozone was both salutary and naturally emitted by the numerous trees in the area (both beliefs later proven false), giving rise to an early name for the region — the "Ozone Belt".

Regular ferry service commenced across Lake Pontchartrain, and shortly thereafter another resort community was founded, Abita Springs. A railroad was constructed in the 1880s connecting Covington and Abita Springs to Mandeville and to New Orleans, allowing for further growth, particularly in Abita Springs, where underground spring waters permitted supposedly healthful baths.

20th century

thumb|Round-trip trolley ticket on the St. Tammany and New Orleans Railways and Ferry Co., punched to be good on the transit line between [[Mandeville, Louisiana|Mandeville and Covington, Louisiana, for the date of December 30, 1915]]

With the completion of high-speed road connections to St. Tammany from New Orleans and its older suburbs (Lake Pontchartrain Causeway, the I-10 Twin Span Bridge), the parish began to develop as a bedroom community. Suburban sprawl first took root in and around Slidell, Louisiana, in the eastern part of the parish. Though the Causeway was completed in 1956 and linked suburban Metairie with western St. Tammany, growth in and around western St. Tammany towns like Mandeville, Covington, and Madisonville only gathered momentum in the late 1960s.

21st century

While St. Tammany was sparsely populated and almost wholly rural in the 1950s, its population exceeded 200,000 in the wake of Hurricane Katrina's landfall in 2005.

A major event in the parish's transition from a bedroom community of commuters to a more diverse and independent economic unit occurred in 2008 with the relocation of Chevron's regional corporate headquarters from downtown New Orleans to an office park outside of Covington.

One of the parish's most powerful figures was Jack Strain, who served as St. Tammany sheriff from 1996 to 2016. After losing his bid for a sixth term, Strain was the subject of a federal corruption investigation into his privatizing a parish work release program in exchange for kickbacks. After being charged with 16 federal counts, Strain agreed to plead guilty to one count of bribery. But the federal investigation also uncovered accusations of sexual abuse involving juveniles. Strain was charged with four counts of aggravated rape, two counts of aggravated incest and one count each of sexual battery and indecent behavior with a juvenile. In 2021, he was found guilty on all counts and sentenced to four life terms in prison.

Hurricane Katrina effects

Hurricane Katrina made its final landfall in eastern St. Tammany Parish. The western eye wall passed directly over St. Tammany Parish as a Category 3 hurricane at about 9:45 AM CST, August 29, 2005. The communities of Slidell, Avery Estates, Lakeshore Estates, Oak Harbor, Eden Isles and Northshore Beach were inundated by the storm surge that extended over inland. The storm surge impacted all of St. Tammany Parish's coastline, including Lacombe, Mandeville and Madisonville. The storm surge in the area of the Rigolets Pass was estimated at , not including wave action, declining to at Madisonville. The surge had a second peak in eastern St. Tammany as the westerly winds from the southern eye wall pushed the surge to the east, backing up at the bottleneck of the Rigolets Pass.

The twin spans of I-10 bridges between Slidell and New Orleans East were virtually destroyed, and much of I-10 in New Orleans East was under water. The Lake Pontchartrain Causeway and the U.S. Highway 11 bridge, connecting the north and south shores of Lake Pontchartrain, were open only to emergency traffic.

Initial search and rescue operations were conducted south of U.S. Highway 190 from Lacombe east to the state line. Fire District No. 1 and the St. Tammany Parish Sheriff's office evacuated over 3,000 people from flooded homes and rescued about 300 people in imminent danger. Radio communications among first responders functioned throughout the rescue period, but the 9-1-1 system was not operational for ten days. Utility services were not available anywhere in the parish. Generator power was available for hospitals and a special needs shelter. Hospitals were running at capacity on generator power.

The hurricane-force winds toppled trees and telephone poles parish-wide, blocking all transportation routes. Land debris cleanup continued into 2007, with over 6.6 million cubic yards (5&nbsp;million m<sup>3</sup>) collected. Debris cleaning in waterways continued at least through 2009.

Hurricane Katrina damaged 48,792 housing units in St. Tammany Parish from flood waters, high winds, or both.

Geography

According to the U.S. Census Bureau, the parish has a total area of , of which is land and (25%) is water. It is located to the north of Lake Pontchartrain.

Major highways

  • 25px Interstate 10
  • 25px Interstate 12
  • 25px Interstate 59
  • 25px U.S. Highway 11
  • 25px U.S. Highway 90
  • 25px U.S. Highway 190
  • 25px Louisiana Highway 21
  • 25px Louisiana Highway 22
  • 25px Louisiana Highway 25
  • 25px Louisiana Highway 36
  • 25px Louisiana Highway 40
  • 25px Louisiana Highway 41

Adjacent counties and parishes

  • Washington Parish (north)
  • Pearl River County, Mississippi (northeast)
  • Hancock County, Mississippi (east)
  • Orleans Parish (south)
  • Jefferson Parish (southwest)
  • St. Bernard Parish (southeast)
  • Tangipahoa Parish (west)

National protected areas

  • Big Branch Marsh National Wildlife Refuge
  • Bogue Chitto National Wildlife Refuge (part)

State protected areas

  • Pearl River Wildlife Management Area
  • Lake Ramsey Savannah Wildlife Management Area

State parks

  • Fairview-Riverside State Park
  • Fontainebleau State Park

Communities

thumb|upright=1.35|Map of St. Tammany Parish, with municipal labels

Cities

  • Covington (parish seat)
  • Mandeville
  • Slidell (largest municipality)

Towns

  • Abita Springs
  • Madisonville
  • Pearl River

Villages

  • Folsom
  • Sun
Census-designated places
  • Eden Isle
  • Lacombe
  • Lewisburg
Unincorporated communities
  • Alton
  • Audubon
  • Barker's Corner
  • Big Branch
  • Blond
  • Bonfouca
  • Bush
  • Chinchuba
  • Colt
  • Crawford Landing
  • Dave
  • Davis Landing
  • Florenville
  • Goodbee
  • Haaswood
  • Houltonville
  • Hickory
  • Maude
  • McClane City
  • Morgan Bluff
  • North Slidell
  • Oaklawn
  • St. Benedict
  • St. Joe
  • St. Tammany
  • St. Tammany Corner
  • Talisheek
  • Waldheim
  • White Kitchen

Demographics