"Cohabitation in the "United States is loosely defined as two or more people, in an "intimate relationship, who live together and share a common domestic life but are neither joined by marriage nor a civil union. Cohabitation of unmarried couples totals about 8.1 million couples who live together in the United States as of 2011.["citation needed]
In most parts of the United States, there is no legal registration or definition of cohabitation, so demographers have developed various methods of identifying cohabitation and measuring its prevalence. The "Census Bureau, currently describes an "unmarried partner" as a "person age 15 years and over, who is not related to the householder, who shares living quarters, and who has a close personal relationship with the householder." Before 1995, the Bureau identified any "unrelated" "opposite-sex couple living with no other adults as ""POSSLQs", or Persons of Opposite Sex Sharing Living Quarters. and the Bureau still report these numbers to show historical trends. However, such measures should be taken loosely, as researchers report that cohabitation often does not have clear start and end dates, as people move in and out of each other's homes and sometimes do not agree on the definition of their living arrangement at a particular moment.
In 2005, the Census Bureau reported 4.85 million cohabiting couples, up more than ten times from 1960, when there were 439,000 such couples. The 2002 National Survey of Family Growth found that more than half of all women aged 15 to 44 have lived with an unmarried partner, and that 65% of American couples who did cohabit got married within 5 years.
In 2011, the Census Bureau reported 7.6 million opposite-sex cohabiting couples in the country with a separate report listing the number of cohabiting same-sex couples at 514,735 as of the "2010 Census.
The cohabiting population includes all age groups, but the average cohabiting age group is between 25-34.
In 2003 a study was made of premarital cohabitation of women who are in a monogamous relationship. The study showed "women who are committed to one relationship, who have both premarital sex and cohabit only with the man they eventually marry, have no higher incidence of divorce than women who abstain from premarital sex and cohabitation. For women in this category, premarital sex and cohabitation with their eventual husband are just two more steps in developing a committed, long-term relationship." Teachman's findings report instead that "It is only women who have more than one intimate premarital relationship who have an elevated risk of marital disruption. This effect is strongest for women who have multiple premarital coresidental unions."
A "survey, conducted by researchers at the University of Denver (2009), of over 1,000 married men and women in the United States found those who moved in with a lover before engagement or marriage reported significantly lower quality marriages and a greater possibility for splitting up than other couples. About 20 percent of those who cohabited before getting "engaged had since suggested "divorce - compared with only 12 percent of those who only moved in together after getting engaged and 10 percent who did not cohabit prior to marriage.</ref>name="telegraph.co.uk"/>
"Psychologist Dr. Galena Rhoades said: "There might be a subset of people who live together before they got engaged who might have decided to get "married really based on other things in their "relationship - because they were already living together and less because they really wanted and had decided they wanted a future together. We think some couples who move in together without a clear commitment to marriage may wind up sliding into marriage partly because they are already cohabiting."
Some people["who?] have claimed that those who live together before marriage report having less satisfying marriages and have a higher chance of separating. A possible explanation for this trend could be that people who cohabit prior to marriage did so because of apprehension towards commitment, and when, following marriage, marital problems arose (or, for that matter, before marriage, when relationship problems arose during the cohabitation arrangement), this apprehension was more likely to translate into an eventual separation. It should be noted this model cites antecedent apprehension concerning commitment as the cause of increased break-ups and cohabitation only as an indicator of such apprehension. Another explanation is that those who choose not to cohabit prior to marriage are often more conservative in their religious views and may hold more traditional views on gender roles, a mindset that might prevent them from divorcing for religious reasons or confronting crisis in relationships despite experiencing marital problems no less severe than those encountered by former cohabitants.["citation needed]
In addition, the very act of living together may lead to attitudes that make happy marriages more difficult.["citation needed] The findings of one recent study, for example, suggest "there may be less motivation for cohabiting "partners to develop their conflict resolution and support skills." (One important exception: cohabiting couples who are already planning to marry each other in the near future have just as good a chance at staying together as couples who don’t live together before marriage).
A 2001 study of 1,000 adults indicated that people who cohabited experienced a "divorce rate 50% higher after marriage than those who did not, though this may be "correlation and not cause-and-effect. A subsequent study performed by the National Center for Health Statistics with a sample size of over 12,000 individuals found that there was no significant difference in divorce rate between cohabitating and non-cohabitating individuals.
In 2011, "The National Marriage Project reported that about 2⁄3 of children with cohabiting parents would see them break up before they were 12 years old. About 1⁄4 of children of married couples would experience this by age 12. Although the chance of divorce increases for longer marriages in general, the divorce rates are not significantly different for those who cohabit prior to marriage and those who do not.  Overall, cohabitation prior to marriage does not appear to negatively impact the chances of future marriage dissolution.
Some places, including the state of California, have laws that recognize cohabiting couples as ""domestic partners". In California, such couples are defined as people who "have chosen to share one another's lives in an intimate and committed relationship of mutual caring," including having a "common residence, and are the same sex or persons of opposite sex if one or both of the persons are over the age of 62". This recognition led to the creation of a Domestic Partners Registry, granting them limited legal recognition and some rights similar to those of married couples.
Two states, "Mississippi and "Michigan, have laws on their books against cohabitation by opposite-sex couples. Anti-cohabitation laws are often not enforced although until recently,["when?] cohabitants were regularly being charged with misdemeanors in Florida.  On March 22, 2016, the Florida legislature voted to repeal the state's ban on cohabitation. The Florida Governor Rick Scott signed the bill into law on 6 April 2016.  Many legal scholars believe that in light of in "Lawrence v. Texas, such laws making cohabitation illegal are unconstitutional (North Carolina Superior Court judge Benjamin Alford struck down the North Carolina law as unconstitutional on that basis). The "Supreme Court of Virginia found the commonwealth's (unenforced["citation needed]) law making fornication (sex between unmarried persons) illegal to be unconstitutional in "Martin v. Ziherl.
The IRS will not grant exemptions for a cohabiting dependent and relatives if cohabitation is illegal in the local jurisdiction.
The charge of "unlawful cohabitation" was used in the late 19th century to enforce the "Edmunds Act, and other federal "anti-polygamy laws against the Mormons in the "Utah Territory, imprisoning more than 1,300 men. However, incidents of cohabitation by non-polygamists were not charged in that territory at that time. Some modern scholarship suggests the Edmunds Act may be unconstitutional for being in violation of the "Free Exercise Clause, although the Supreme Court has repeatedly ruled that neutral laws that happen to impinge on some religious practices are constitutional.