There is no state or territory of the United States with the name Jefferson — but there were four such entities that either existed or were contemplated in the course of American history. If someone mentions the state of Jefferson that existed in an alternate universe, the question should be: which one?
The Territory of Jefferson existed from 1859 for about eighteen months, and was an enormous rectangular-square of the frontier that contained all of present-day Colorado and parts of Utah, Wyoming, Kansas and Nebraska. It was never recognized by the federal government, although it had a functioning local government during the course of its existence. It was organized by the federal government into the Territory of Colorado as its successor.
In 1870, during the Reconstruction following the Civil War, the northern-dominated Republican Congress tried to divide Texas into three states. Today, the northerns are probably delighted that they failed, as this would have only meant more Senators from the region elected to Congress, but at the time, the fear was that a united Texas would be strong enough to declare independence and form the backbone of a new confederate resistance. So a bill was introduced in Congress that would split the state into three — central Texas remaining as Texas, the state of Matagorda west of the Colorado river, and the state of Jefferson east of the San Antonio river. That bill died, but how to divide Texas to keep it more… manageable was a question that persisted. In 1906, Congress proposed that Texas establish four independent legislatures on a regional basis, all functioning under one governor. According to the plan the state was to have eight senators, but the proposal met with only passing interest in Texas and no favorable action from Congress.
A few decades later, Texas tried to divide itself a few times in some attempts that were constitutionally permitted but never taken all that seriously. This is because the Act of Admission of Texas into the Union allows the state to divide itself. The closes this ever came to becoming a reality was a bill introduced to the Texas legislature in 1915 in order to create a State of Jefferson, made up of the Texas Panhandle. This proposal had only minimal support in the region and the proposal never really got off the ground.
The most dramatic and interesting attempt at a State of Jefferson was the secession movement in Oregon and California in October 1941. Then, Mayor Gable of Port Orford in Oregon announced that several Oregon counties should join with northern California counties to form a new state, with the proposed name of Jefferson. The common bond was that the people throughout the region found their state legislatures as indifferent to local needs. In somewhat quaint American provincialism, in late November 1941, a group of young men gained national media attention when, brandishing hunting rifles, they stopped traffic on U.S. Route 99 south of Yreka, and handed out copies of a Proclamation of Independence, stating that the state of Jefferson was in “patriotic rebellion against the States of California and Oregon”… and would continue to secede, every Thursday, until further notice!
But it all came to an abrupt end when Mayor Gable died on 2 December, just weeks after commencing his secessionist movement, and Pearl Harbor was struck on 7 December, channeling the efforts of secessionists on the war effort. Coincidentally, the “state of Jefferson” was one of the few places in the continental USA to be bombed during World War II, when a Japanese pilot dropped bombs on the Oregon Coast near Brookings in September 1942.