The Territorial Counties dropdown used to search the Nebraska Legislators, Past and Present database includes the counties that were represented in the Territorial House and Council. The Territorial House and Council were in place between 1857 and 1867. Looking through the list of counties you may notice a few unique county names. These counties include: Calhoun, Forney, Green, Jones, L'Eau qui Court and Monroe. A brief history of these counties can be found in the book Johnson's history of Nebraska by Harrison Johnson, copyright 1880.
Calhoun County (page: 533)
“Saunders County, formerly called Calhoun, was created in 1856. By an Act of the Legislature, approved January 8, 1862, its name was changed to Saunders, in honor of Hon. Alvin Saunders, the last Territorial Governor and present United States Senator from Nebraska.”
Forney County (page: 456)
"Nemaha, in the first organization of the Territory, was called Forney County. It was re-organized by the First Territorial Legislature, under its present name."
Green County (page: 556)
"Seward, formerly Green County, was created in 1855 and organized in 1865. Its name was changed by an Act of the Legislature in 1862, in honor of Hon. Wm. H. Seward, the distinguished statesman."
Jones County (pages: 399-400)
"Jefferson County was mapped out by the Territorial Legislature, January 26, 1856, under the name of Jones County. At the same time the adjoining county on the west, now Thayer County, received the name of Jefferson. Eight years after, 1864, Jefferson County organized by holding its first election at Big Sandy. An “Act to Enlarge Jefferson County” passed the Legislature on the 18th of February, 1867, uniting Jones to Jefferson County. This union continued until the Legislature of 1870-71 provided by enactment of the division of Jefferson County, which event was consummated in the fall of 1871 by the election of two sets of County Officers, the Sixth Principle Meridian being the dividing line. The former Jones, in the divorcement, retaining the name of Jefferson, and the former Jefferson assuming the name Thayer.”L'Eau qui Court County (page: 425)
“Knox County was organized under the name of L’eau qui Court by the Territorial Legislature of 1856-7. In February, 1873, the Legislature changed its name to Knox.”
Monroe County (page: 498 )
"The first election in Monroe County was also the last; for in the winter session of the Territorial Legislature of 1858-9, on joint petition of the two Counties, Monroe was consolidated with Platte County."
Another county you should note is Clay County. Although there is currently a Clay County in Nebraska the one of territorial times is not the county we know today. In approximately 1855 Clay County was located between present day Gage and Lancaster counties. In 1864 the then Clay County was divided between Gage and Lancaster counties. More information about the history of the original Clay County can be found starting on page 41 in the book History of Gage County, Nebraska by Hugh Jackson Dobbs, copyright 1918.
Other county boundaries have also changed over time. To see how the county boundary lines have moved take a look at this Colton's Kansas and Nebraska map from 1858.