Admitted to the Union on April 30, 1812 as the 18th state. As part of the Louisiana Purchase, Orleans Territory was created in 1804 and was distinct from the Louisiana Territory of 1805—1812 in present-day Missouri and Arkansas. Due to its French origins, Louisiana has parishes rather than counties.
- 1810 – 1940 federal censuses extant for all parishes with the exception of those noted below:
- All parishes extant in 1860 census except for Bienville.
- All parishes lost for 1890 census.
| Acadia | Allen | Ascension | Assumption |
| Avoyelles | Beauregard | Bienville | Bossier |
| Caddo | Calcasieu | Caldwell | Cameron |
| Catahoula | Claiborne | Concordia | De Soto |
| East Baton Rouge | East Carroll | East Feliciana | Evangeline |
| Franklin | Grant | Iberia | Iberville |
| Jackson | Jefferson | Jefferson Davis | La Salle |
| Lafayette | Lafourche | Lincoln | Livingston |
| Madison | Morehouse | Natchitoches | Orleans |
| Ouachita | Plaquemines | Pointe Coupee | Rapides |
| Red River | Richland | Sabine | St. Bernard |
| St. Charles | St. Helena | St. James | St. John The Baptist |
| St. Landry | St. Martin | St. Mary | St. Tammany |
| Tangipahoa | Tensas | Terrebonne | Union |
| Vermilion | Vernon | Washington | Webster |
| West Baton Rouge | West Carroll | West Feliciana | Winn |