You do not need to be a resident of NH in order to be legally married in NH.* A marriage application may be filed for in any town or city within the state of New Hampshire.
*No marriage by parties residing outside of NH shall be construed as legal if the jurisdiction they live in would interpret such a marriage as null and void. This also applies to residents of NH if they are married outside of NH jurisdiction and NH would interpret the marriage as null and void.
It is not legal in the state of NH to marry your first cousin or anyone in closer kinship to you. It is not legal to be married in the state of NH if you are under the age of 18. Exceptions are made if you are a female between the ages of 13 and 17 or a male between the ages of 14 and 17 and have obtained parental permission and a waiver from a superior court or probate court judge.