Much like every state has its own distinct driving, property, and family laws (among many others), each one is likewise permitted to have individual laws pertaining to gay marriage, same-sex civil unions, and other forms of government-sanctioned partnerships.
Although the 1996 Defense of Marriage Act, or DOMA, prohibits same-sex partnerships from being legally recognized by the federal government- specifically, it states that 1.) No state, U.S. subdivision or jurisdiction needs to treat a same-sex relationships the same sex as a heterosexual marriage, even if it is considered equal to a marriage in another state, and that 2.) The federal government recognizes a legal marriage solely as a union between one woman and one man. Certain states, such as Connecticut, Iowa, Massachusetts, New Hampshire, Vermont, and the District of Columbia, have indeed made the move to grant legal gay marriage rights for the homosexual community on a state level.
In these cases, gay marriages are entitled to receive the 400 or so benefits which are granted to married couples within the borders of the state, however, are restricted from having access to the full 1,100 or so federal rights and protections which heterosexual married partnerships enjoy.
As for those states which have not yet recognized gay marriages, but rather, have opted for creating a civil union law in respect of its gay, marriage-minded couples and these include California, Colorado, Hawaii, Maine, New Jersey, Nevada, Oregon, Washington, and Wisconsin.
The legal rights and benefits vary greatly from state to state. When Vermont became the first U.S. state to sign a civil union bill into law in 2000, for instance, couples were able to enjoy nearly every one of the privileges that non-gay marriages had, except for four (two of which pertained to adoption).
Being that the state gave full martial rights to homosexual partnerships through a gay marriage law enacted in 2009, however, civil unions have since then become unnecessary for the Vermont gay community, and every civil union has officially been recognized as a legal gay marriage, with all of the attached legal benefits. States such as New Jersey and Nevada also provide civil unions with all the full rights and benefits of state marriages.
In other cases, however, civil union laws or domestic partnership laws offer only a small fraction of the benefits which the state government would otherwise provide for couples in a heterosexual marriage. This is clearly seen in Wisconsin, which provides only 43 rights and protections to it’s same-sex couples, in contrast to over 200 which married couples in the state receive.