Proposals for new US states

Almost since the formation of the USA as a union of thirteen states, there have been arguments about splitting or combining states into new entities. The most famous proposal is probably the State of Jefferson made up of parts of California and Oregon. There have been other plans to partition California and Texas, two of the largest and most populous states, and to divide other states in more or less logical ways.

State of Jefferson
The State of Jefferson is a proposed new state in the United States which would consist of the counties presently in far northern California and southwestern Oregon.

The State of Jefferson was first proposed by the mayor of Port Orford, Oregon, in October 1941, and the idea actually got the endorsement of several county governments in the region. The movement got as far as the selection of Yreka (Siskiyou County, California) as the provisional state capital and Jefferson as the name of the new state, but the attack on Pearl Harbor in December brought the movement to an abrupt halt.

The influence of the original proposal remains in the local National Public Radio network calling itself Jefferson Public Radio, and one Oregon highway officially named the State of Jefferson Scenic Byway. Signs can also be seen along northern California highways calling for the state's formation, showing "The Great Seal of the State of Jefferson," a stylized gold-mining pan with two X's on it.

The idea has recently been revived and appears mainly to be motivated by property rights concerns and conservative unhappiness with the perceived liberal bent in the California and Oregon state governments. After the election of Donald Trump in 2016, liberals called for the secession of California from the United States (CalExit), but Trump supporters in the north of the state saw this as another reason to detach from liberal California.

In 2018, Citizens for Fair Representation, led by Mark Baird of the State of Jefferson movement, litigated to try to increase the size of California's senate by adding 1200 members to represent the 90-fold increase in California's population since California's legislature was originally created; they lost the case. It's unclear if this was a deliberate attempt to sabotage the Californian state government or some other form of protest.

Under the United States Constitution, "no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress." (Article IV, Section 3, Clause 1).

California multiplication
Dividing California into two or three states (or even six) has been proposed several times. California was originally partitioned by the Mexicans in 1804 into Alta California (now part of the US) and Baja California (still part of Mexico). In 1855, the California State Assembly passed a resolution calling for trisection, creating new states called Shasta in the north and Colorado (not the current state) in the south, but it died due to legislators having other priorities. The Pico Act in 1859 called for the region south of the 36th parallel to become a new territory; it actually passed at the ballot and was signed by the governor, but by then the U.S. Congress had other things on its mind and did not approve it.

In 1965, state senator Richard J. Dolwig proposed a split 100 miles north of Los Angeles; it passed in the State Senate but ground to a halt in committee. A failed ballot measure during the 1990s would have split California into three states; proposed by Stan Statham, it called for a non-binding referendum but was killed in committee. There was another proposal around 2011 to separate conservative-leaning counties of Southern California (excluding areas like Los Angeles County) from the rest of California over the liberal politics of Sacramento, but this failed to garner any support. Tech venture capitalist, Bitcoin proponent, and self-proclaimed inventor of viral marketing tried to get a "Six Californias" proposal on the 2016 ballot but also failed. Draper proposed the generally boring names of Jefferson, North California, Silicon Valley, Central California, West California, and South California for the new states.

Texas
Texas was given the right to split into five when it joined the US in 1845. This has been occasionally suggested to increase its power in the Senate and Electoral College, as well as to help underrepresented areas, mainly in the west. The US Congress rejected one 1869 proposal for the State of Lincoln south and west of the Colorado River, but other proposals (including panhandle secession in 1915 and 1935 plans for Texlahoma) didn't get that far; today nobody wants to mess with Texas.

State of Superior
Michigan is divided into two parts by the Great Lakes, and the State of Superior is a hypothetical proposal for the upper peninsula of Michigan, sometimes also including a few counties in northern Wisconsin that are culturally and geographically similar. Its rural character is very different from the area around Detroit, and secession of the upper peninsula (and possibly part of the "mitten") was seriously attempted in the Michigan legislature in the 1970s but failed to get enough support to get on the ballot. With just over 300,000 people, it would be the least-populated state in the Union, and its viability and tax base are uncertain. According to Wikipedia, there is no current movement for a new state.

Other proposals

 * State of Lincoln (eastern Washington and the Idaho panhandle)
 * State of Kootenai (western Montana and the Idaho panhandle)
 * State of Absaroka (parts of Montana, South Dakota, and Wyoming) — in 1939, opposed to the New Deal and the Democrat governor of Wyoming.
 * State of Franklin (western North Carolina and upper east Tennessee, west of the Appalachians). Franklin was an independent nation for a short time after the American Revolutionary War from 1784 to 1789, in land ceded by North Carolina, with its capital at Jonesborough and then Greeneville. But most of its territory actually belonged to the Muskogee and Cherokee, who transacted treaties with the new United States rather than the government of Franklin; unable to secure its territory, Franklin fell apart and its counties rejoined North Carolina.
 * New York City and/or Long Island splitting from New York state, and upstate/western New York trying to do the same (possibly to be called Niagara). Norman Mailer was one of the more prominent advocates of statehood for New York City, campaigning in the 1969 Democratic Mayoral Primary. In the 2010s, a new impetus was found for secession when Andrew Cuomo banned fracking in the state, and counties with significant frack resources sought a new home.
 * Combining North Dakota and South Dakota into the single State of Dakota, possibly called MegaKota. This seems more a meme than a serious proposal, despite 3000 petition signatures in 2019.
 * Southern Arizona (Pima County, Santa Cruz County, and Cochise County) - separating off the more liberal and immigrant-friendly parts as Baja Arizona or (less euphoniously) Gadsden. Confederate Arizona wasn't a big success, but this plan is to escape the racists in the north.
 * South Florida, which contains most of the state's population and is more concerned with global warming and rising ocean levels than the government in distant, northern Tallahassee.
 * The State of Westmoreland was proposed in 1784 to try to settle land disputes between Pennsylvania and Connecticut.
 * Republic of Winston: there is a bit of a myth that Winston County, Alabama, is said to have seceded from Alabama in protest of the state's secession to join the Confederacy; in fact, while it was discussed early in the Civil War, it never got very far; the claim has been subsequently exaggerated for tourism. Nearby regions of northern Alabama and Tennessee considered seceding under the name of Nickajack, but this never came to fruition either.
 * Free State of Jones: allegedly proclaimed by Civil War-era deserters in Mississippi, again they didn't get very far beyond drinking a lot and proclaiming themselves free.
 * "New Nevada" (Nevada without Clark County) and "New California" (California without the urban areas), two imaginary states that tried to side with Texas in order to overturn the results of the 2020 US presidential election.
 * Making the consisting of parts of Arizona, New Mexico, and Utah, its own state has also been proposed.

Naming
Coming up with a cool name is one of the hardest parts of formulating your state proposal. One of the most common sources seems to be the names of popular presidents and Founding Fathers, hence Jefferson, Lincoln, and Franklin. Rivers and lakes are also quite popular, although many already have states named after them (Mississippi, Missouri, Ohio, Tennessee, Colorado, Arkansas, Delaware, Michigan) so the pool is limited. Absaroka and Kootenai were proposals named after Native American tribes, which has also been the source of several actual state names. The last resort is "north/south/east/west X" which was good enough for the Dakotas and Carolinas, but in these days when states compete fiercely for inward investment, something more catchy is probably required. California was apparently named after a fictional island in a then-popular novel, while the name Idaho was completely made up, so really the sky is the limit.