Jefferson Parish was named in honor of U. S. President Thomas Jefferson of Virginia when the parish was established by the Louisiana Legislature on February 11, 1825, a year before Jefferson died. A bronze statue of Jefferson stands at the entrance of the General Government Complex on Derbigny Street at the parish seat in Gretna. The parish seat was in the City of Lafayette, until that city was annexed by New Orleans in 1874.

Originally, this parish was larger than it is today, running from Felicity Street in New Orleans to the St. Charles Parish line. However, as New Orleans grew, it absorbed the cities of Lafayette, Jefferson, Carrollton and several unincorporated areas (faubourgs). These became part of Orleans Parish. The present borders between Jefferson Parish and Orleans Parish were set in 1874. The Jefferson Parish seat was moved to Gretna at the same time. Note: The "City of Lafayette" in Jefferson Parish, as it is recorded in U.S. censuses until 1870, should not be confused with the present city of Lafayette, Louisiana in Lafayette Parish.

From the 1940s to the 1970s, Jefferson's population swelled with an influx of middle-class white families from Orleans Parish. The parish's population doubled in size from 1940 to 1950 and again from 1950 to 1960 as the parents behind the post–World War II baby boom, profiting from rising living standards and dissatisfied with their old neighborhoods, chose relocation to new neighborhoods of detached single-family housing. By the 1960s, rising racial tensions in New Orleans complicated the impetus behind the migration, as many new arrivals sought not only more living space but also residence in a political jurisdiction independent from New Orleans proper.

The earliest postwar subdivisions were developed on the Eastbank of Jefferson Parish ("East Jefferson") along the pre-existing Jefferson Highway and Airline Highway routes, often relatively far-removed from the New Orleans city line, as land prices were lower further away from New Orleans and land assembly was easier. The completion of Veterans Highway in the late 1950s, following a route parallel to Airline but further north, stimulated more development. The arrival of I-10 in the early 1960s resulted in the demolition of some homes in the Old Metairie neighborhood, where development began in the 1920s, but resulted in even easier access to suburban East Jefferson.

In the portion of Jefferson Parish on the Westbank of the Mississippi River ("West Jefferson"), large-scale suburban development commenced with the completion, in 1958, of the Greater New Orleans Bridge crossing the Mississippi River at downtown New Orleans. Terrytown, within the city limits of Gretna, was the first large subdivision to be developed. Subsequent development has been extensive, taking place within Harvey, Marrero, Westwego and Avondale.

Similar to the development trajectory observed by other U.S. suburban areas, Jefferson began to enjoy a significant employment base by the 1970s and 1980s, shedding its earlier role as a simple bedroom community. In East Jefferson, the Causeway Boulevard corridor grew into a commercial office node, while the Elmwood neighborhood developed as a center for light manufacturing and distribution. By the mid-1990s, Jefferson Parish was exhibiting some of the symptoms presented by inner-ring suburbs throughout the United States. Median household income growth slowed, even trailing income growth rates in New Orleans proper, such that the inner city began to narrow the gap in median household income, a gap at its widest at the time of the 1980 Census. St. Tammany Parish and, to a lesser extent, St. Charles Parish began to attract migrants from the inner city, and increasingly even from Jefferson Parish itself. These trends were catalyzed by Hurricane Katrina, which destroyed much of New Orleans' low-income housing and propelled further numbers of lower-income individuals into Jefferson Parish. Despite these challenges, Jefferson Parish still contains the largest number of middle class residents in metropolitan New Orleans and acts as the retail hub for the entire metro area.

Even though Jefferson Parish was affected by Hurricane Katrina, it has rebounded more quickly than Orleans Parish, since the devastation was not as severe. The parish has a current population of 440,000, which is 15,000 fewer people than was recorded by the 2000 U.S. Census. New Orleans' Katrina-provoked population loss has resulted in Jefferson Parish becoming the most populous parish tying with East Baton Rouge Parish, center of the Baton Rouge metropolitan area.

Crucially, Jefferson's levees and floodwalls did not fail in the wake of Katrina, enabling floodwaters to be rapidly pumped out. As of October 2006, Jefferson Parish had, in effect, completely rebounded from Hurricane Katrina, while far more damaged Orleans Parish continued recovering at a slower rate. Estimates of Jefferson Parish's population ranged from 420,000 to 440,000, and this figure was expected to continue to rise as evacuated residents from Orleans Parish returned to metropolitan New Orleans.

The parish has a total area of 642 square miles, of which 307 square miles is land and 336 square miles (52.29%) is water. The population recorded in the 1830 Federal Census was 6,846. The 2010 census recorded 432,552 residents in the Parish.

Neigboring parishes are Orleans Parish (East), St. Bernard Parish (East), Plaquemines Parish (East), Lafourche Parish (West), and St. Charles Parish (West). Communities in the parish include Metairie, Kenner, River Ridge, Jefferson, Harahan, Elmwood, Marrero, Terrytown, Harvey, Gretna, Estelle, Woodmere, Timberlane, Westwego, Waggaman, Bridge City, Avondale, Jean Lafitte, Barataria, Crown Point, Grand Isle, and Lafitte.

Birth Records - The Louisiana State office maintains records for 100 years after the date of birth. Birth records are considered confidential for the first 100 years. For current information on who may obtain a birth record as well as how to submit a request visit the Office of Public Health, Vital Records Registry website or write to them at PO Box 60630, New Orleans, LA 70160.

Birth records older than 100 years are available through the Louisiana State Archives, 3851 Essen Lane, Baton Rouge, LA 70809. (225) 922-1000.

Death Records - The Louisiana State office maintains records for 100 years after the date of death. Death records are considered confidential for the first 100 years. For current information on who may obtain a death record as well as how to submit a request visit the Office of Public Health, Vital Records Registry website or write to them at PO Box 60630, New Orleans, LA 70160.

Death records older than 100 years are available through the Louisiana State Archives, 3851 Essen Lane, Baton Rouge, LA 70809. (225) 922-1000.

Marriage Records - For current information on how to submit a request for a certified copy of an Orleans Parish marriage record less than 50 years old, see the Louisiana Office of Public Health Director, Vital Records and Statistics website or write to PO Box 60630, New Orleans, LA 70160.

Certified copies for the parish are issued by Clerk of Court. For the address of the parish Clerk of Court visit the Jefferson Parish Important Addresses page.

Marriage records over 50 years are stored by the Louisiana State Archives, 3851 Essen Lane, Baton Rouge, LA 70809. (225) 922-1000.

Divorce Records - To obtain current information on how to submit a request for a certified copy of divorce records contact the Clerk of Court. For the address of the parish Clerk of Court visit the Jefferson Parish Important Addresses page.