The Jefferson County Courthouse is located at 210 Courthouse Way, Rigby, ID 83442; phone: 208-745-8111.
Several early expeditions passed through this area including the Coulter party in 1808 and Captain Bonneville in 1832.
White trappers frequently stopped at the Indian Camping ground around what was then called Market Lake (Roberts) because of an abundant supply of game.
One of the earliest settlements was located there. This eventually became an important stage depot for the Union Pacific. Other stage and freight stations were established at Sand Hole and Lava under the auspices of the Eastern Pony Express in 1864 and later Wells Fargo.
Lava (Camas) was especially busy as an ore loading point during Idaho's silver mining period, although Jefferson County never experienced a mining boom.
The earliest permanent settlers in the region were Utah Mormons who arrived in the 1870's and 1880's and set up irrigation systems and established prosperous farming communities. Annis, Menan, Lewisville and Lorenzo all in the Snake River Valley, were among the early settlements. In addition to land irrigated from Mud Lake and the Snake River, the drier areas were utilized by the early farmers for livestock raising and dairying, as well as some dry farming.
Roberts (the first settlement in the county), Annis, Menan, Lewisville, Lorenzo and Labelle were among the early settlements.
Thomas R. Hamer, an Idaho congressman, said in September 1913 that Fremont County should be divided as it was becoming too costly for the sprawling county. The question of division was submitted at the November 4, 1913 election with the people living within the boundaries of the new county paying for the expense of the election.
If the majority of the votes cast were in the affirmative the governor would appoint officers to serve as of the first Monday in January 1914. The election was held on November 5, 1913 with 1827 votes in favor of the new county and 603 votes in the negative. At this election the voters also voted on the county seat. Rigby received 1,368 votes with Menan receiving 961 votes.
To choose a name for the new county was the first order of business. County Treasurer James J. Chandler read the following from the inaugural address of Thomas Jefferson: "We are about to enter, fellow-citizens, on the exercise of duties which comprehend everything dear and valuable to us, it is proper we should understand that we deem the essential principles of our government, and consequently those which ought to shape its destiny. In honor of this great man I suggest the name for our county be Jefferson County."
It was unanimously voted.
Governor John M. Haines then issued an executive act declaring the creation of Jefferson County. The citizens of Rigby provided the county with a frame courthouse and a lease on the ground for ninety-nine years at a cost of one dollar a year.