There have been many proposals to partition existing states so that regions could secede from one state to join another state, or to create a new state. Partitions and secessions were also proposed during the American Civil War so that regions could declare loyalties to the Union or the Confederacy. Proposals to secede from the Union or to create states from territories are not listed.
In February 2011, Tucson politicians and activists formed the group "Start our State," to advocate secession for Pima County and other southern counties to create a state called "Baja Arizona". The group wanted the Pima County Board of Supervisors to put the issue on the 2012 ballot, but it was rejected by the Board due to lack of authority, so the group circulated petitions. Interest in secession grew when Republican Governor Jan Brewer and her allies enacted Arizona SB 1070, regarding illegal immigration. Furthermore, the state had passed laws affecting Tucson elections and how the city bids for public works projects. A historical justification was found in that the northern part of Arizona was ceded to the United States in 1848, but that the southern part of Arizona, south of the Gila River, was acquired by the United States in 1854 with the Gadsden Purchase.
In the mid-1930s, the Walsenburg World-Independent proposed that Huerfano County secede from the state. This was a pet project of Sam T. Taylor, a sports editor, who went on to become a long-serving state senator, continuing to pursue the idea unsuccessfully.
In 1973, nearby Costilla County had expressed interest in seceding from Colorado and joining New Mexico.
On June 6, 2013, commissioners in Weld County announced a proposal to secede and to form the state of North Colorado, citing concerns with state policy and recently enacted legislation relating to the region’s main economic drivers, including agriculture and energy. The commissioners stated that they would hold public meetings to gather input before crafting a ballot initiative by August 1, and that the proposal had aroused preliminary interest from fellow commissioners in Morgan, Logan, Sedgwick, Phillips, Washington, Yuma and Kit Carson counties.
Politicians in the South Florida metropolitan area have made proposals to split Florida into two states - North Florida and South Florida. One such proposal was made in 2008 by the North Lauderdale commissioners. The idea occasionally pops up in later news articles.
"We'd have Fort Lauderdale, West Palm Beach and Miami. They'd have Orlando, Tampa and Jacksonville. We'd have Donald Trump. They'd have Donald Duck. We'd have the Keys. They'd have the Redneck Riviera. We'd have Big Sugar. They'd have Big Citrus. We'd have the Dolphins and the Hurricanes. They'd have the Gators and the 'Noles. We'd have the Everglades. They'd have Busch Gardens. We'd have casinos. They'd have school prayer. We'd have same-sex marriages. They'd have the defense-of-marriage act." - Michael Mayo, writer for the Sun-Sentinel
In the late 1850s, a local politician threatened to have Dade County secede from the state of Georgia if the latter did not leave the Union. The result was that the area was termed "State of Dade". In 1939, when Georgia purchased land that would become Cloudland Canyon State Park, the State of Dade finally had a road connecting them to Georgia (prior to this, they only had roads to Tennessee and Alabama). In 1945, the State of Dade passed a resolution to officially rejoin Georgia.
In 1925, Cook County considered secession to create the state of Chicago.
In the early 1970s, residents in western Illinois were upset over the allocation of state funds for transportation, prompting a student at Western Illinois University to declare 16 counties the Republic of Forgottonia. Although the declaration was meant to be a joke, the secession idea was picked up by the Western Illinois Regional Council, until State Representative Doug Kane showed that the counties had received funding that was more than what they paid in state taxes.
In November 2011, State Representatives Bill Mitchell and Adam Brown introduced a proposal to make Cook County a state of its own. They felt that all of Illinois outside of Cook County should become a separate state, due to Chicago's "dictating its views" to the rest of the state.
In 1992, a group in southwestern Kansas advocated the secession of a number of counties in that region from the state. Nominally headed by Don O. Concannon, a lawyer and former gubernatorial candidate from Hugoton, the group called the new state name "West Kansas", a state bird (pheasant), and a state flower (yucca). The proposal was in reaction to laws raising real estate taxes, and shifting state education funding away from rural school districts and into more urban areas. Though organizers arranged for a series of straw polls that demonstrated widespread support for secession in nine counties, the movement died out by the mid-1990s.
Maine was initially part of the Commonwealth of Massachusetts before being admitted to the Union as a state in 1820. However, its boundary with British North America (now Canada) had been in dispute for several decades. In 1827, John Baker unilaterally declared the disputed territory (now part of Aroostook County) to be the "Republic of Madawaska". The declaration was rejected by Maine in 1831. Following the undeclared Aroostook War in 1838-39, the United States and United Kingdom signed the Webster-Ashburton Treaty on August 9, 1842 to settle the border issue.
In 1998 and again in 2005, state representative Henry Joy proposed legislation to partition Maine into northern and southern states. He cited concern for the rural northern part being affected by "anti-business policies" and "overzealous environmental safeguards," and related the southern part to an extension of Massachusetts.
In September 2009, Frederick County Commissioner John L. Thompson Jr. proposed that the county should secede from Maryland, on the concern that the county gives more to state government in tax dollars than it receives in services and benefits. The proposal was rejected by the other commissioners in the county.
In February 2014, it was reported that residents from Western Maryland have started petitions to form a new state, citing taxes and gun control as issues. Possible names for such a proposed state included Liberty, Antietam, and Augusta.
Maine, which was physically separate from the rest of Massachusetts, had proposed secession multiple times in the early 19th century, eventually winning approval by Massachusetts in 1819, and a vote by Maine in 1820. The formation of the state of Maine as the 23rd state occurred on March 15, 1820 as one of the provisions of the Missouri Compromise.
In 1977, the islands of Martha's Vineyard, Nantucket, and the Elizabeth Islands proposed to separate from Massachusetts because of a redistricting bill that would have deprived Dukes County, consisting of Martha's Vineyard and the Elizabeth Islands, and Nantucket County of separate representation in the General Court. At local town meetings, culminating in the All-Island Selectmen’s Association Conference, residents and community leaders voted in favor of secession with an "overwhelming majority". When the Nantucket state representative filed a bill with the Massachusetts Legislature, the Governor of Connecticut suggested that the islands join his state, the New Hampshire House of Representatives and the Rhode Island Senate each passed resolutions inviting the islands to join their states, and the Governor of Vermont and the Vermont General Assembly both supported annexation to their state. Although the redistricting bill passed, the state representatives pledged to assign aides for the two counties that would report to their state representative, and the area received much positive publicity.
There has been intermittent advocacy for the Arrowhead of Minnesota, the three northeast counties of the state adjacent to Lake Superior, to join with northwestern Wisconsin and the Upper Peninsula of Michigan to form a new state to be named "North Country" or Superior, with Duluth as its capital.
In the 1990s, Randy Kuhl, from rural upstate Hammondsport, had advocated secession by regularly proposing bills to that effect while he was a state senator. His 1999 bill would have New York City, Long Island, Westchester and Rockland Counties become a separate state of New York, while the rest of the counties would be grouped as West New York.
From 2007-2009, Long Island residents discussed secession on the grounds that their tax money is not used to fund programs in their counties. Proposals were made for the entire island (Kings, Queens, Nassau, and Suffolk counties) and for just the two counties (Nassau and Suffolk).
2010 gubernatorial candidate Carl Paladino's supporters, Rus Thompson and James Ostrowski in the Buffalo region, have supported secession of western New York from New York City and its nearby counties.Fred Smerlas, in discussing a potential platform for a 2010 Congressional run from western New York, stated that he would make the separation of New York City and upstate a top priority: "My first act if I ever got elected would be to take a big saw and cut New York City off."
In 1984, the township of New Shoreham, located on Block Island, threatened to secede because the state had denied them the ability to ban or to control the use of mopeds on the island. Both Massachusetts and Connecticut were reported as having interest in annexing the island. After the town voted to put the issue on the state ballot for June, the Rhode Island government eventually compromised by allowing the island to control the number of mopeds on the island.
Under the joint resolution of Congress, the Republic of Texas joined the Union with the right to partition itself into as many as five states. As a result, Texas "divisionists" would occasionally propose partitioning in its early decades.
In 2002, the United States House of Representatives voted to allow Wendover to leave the state and join Nevada, merging with the city of West Wendover. However, Nevada Senator Harry Reid blocked the bill's consideration in the Senate, citing that it would affect the investments of the casinos in the border town.
In 2008, state representative Neal Hendrickson proposed Joint Resolution 6 (HJR006): "the creation of a separate state, consisting of the southern portion of the present state of Utah with a northern boundary stretching east and west across the present state of Utah at the southern border of Utah County".  The bill did not pass.
In 2004 and 2005, the town of Killington voted to secede from Vermont to join New Hampshire, despite being situated in the center of the state. A similar motion was attempted in Winhall, but was voted down.
On July 21, 1967, the Village of Winneconne seceded to become the Sovereign State of Winneconne in order to protest its omission from the state's highway map. After negotiations restored the village's location, Winneconne rejoined the state. The village has since celebrated the secession with an annual Sovereign State Days event.
Portions of the northern counties were included in proposals for the State of Superior.
Winston County considered seceding from the state in order to remain neutral during the Civil War. This led pro-confederate Richard Payne to call them the "Free State of Winston" or the Republic of Winston.
Five counties, including Madison County voted against secession from the Union at the second Arkansas Secession Convention. When called upon to renege, four counties did, but Madison, represented by Isaac Murphy, later the state's governor under Reconstruction, resisted. Men of his county fought for the North during the war.
Counties in southern Illinois considered secession to join the Confederacy; a proposed name for the new state was Little Egypt after the region's local name. However, speeches by Union General John A. Logan, a native of the region, convinced many in the region to remain in the Union.
On November 20, 1861, Confederate sympathizers, calling themselves the "Convention of the People of Kentucky", met at Russellville to pass an Ordinance of Secession for its regions. This established the Confederate government of Kentucky, which was recognized by the Confederacy. Its capital was Bowling Green.
In 1861, the town of Town Line voted to secede from the Union and join the Confederacy. Although the town sent soldiers to support the Confederate Army over the course of the war, the Confederacy did not officially recognize Town Line as one of its own. During Reconstruction, the secession of Town Line was eventually forgotten, but in the 1920s, Town Line residents still considered themselves "outside the Union" and were not paying taxes. In 1946, after significant media attention, town residents voted to rejoin the Union.
Scott County passed a proclamation to secede from Tennessee and form the "Free and Independent State of Scott" in order to support the Union. When it was discovered in 1986 that this county law was still on the books, the proclamation was finally repealed. The county then petitioned the state of Tennessee for readmission, even though the original secession had not been recognized by the either the state or federal government.
After Virginia declared its secession from the U.S. in 1861, its mountainous western half formed the pro-Union Restored Government of Virginia; the Union Congress recognized this as Virginia's legitimate government, with authority to approve its own partition. In 1863, the area was admitted to the Union as the state of West Virginia.