"[a] Louisiana's usage of the term "parish" for a geographic region or local government dates back to the French colonial and Spanish colonial periods and is connected to ecclesiastical parishes.

The remaining 26 have various other forms of government, including: council-president, council-manager, parish commission, and consolidated parish/city.

[1] Louisiana was formed from French and Spanish colonies, which were both officially Roman Catholic.

The borders of these counties were poorly defined, but largely coincided with the colonial ecclesiastical parishes.

[2][3] On March 31, 1807, the territorial legislature created 19 parishes without abolishing any of the old counties (which term continued to exist until 1845).

(A surveying error in Iberia's creation broke St. Martin Parish into two non-contiguous parts, making it and Norfolk County, Massachusetts as the only county-level units with their own exclaves.)

There were several minor boundary changes afterward, the most substantial being the division of Lake Pontchartrain among Tangipahoa, St. Tammany, Orleans, Jefferson, St. John the Baptist, and St. Charles Parishes in 1979.

[2] The original twelve counties defined by the Territorial Legislative Council in 1805 were:[2] On December 7, 1810, William C. C. Claiborne, governor of the Orleans Territory, annexed the short-lived Republic of West Florida to the United States and Louisiana as Feliciana County.

On December 22, 1810, the county west of the Pearl River was organized in four civil parishes: East Baton Rouge, Feliciana, St. Helena, and St. Tammany.