An unmarried partner is a person aged 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. Responses of same-sex spouse are edited into this category.

The data on relationship to householder were derived from answers to Question 2, which was asked of all people in housing units. One person in each household is designated as the householder. In most cases, this is the person, or one of the people, in whose name the home is owned, being bought, or rented and who is listed on line one of the questionnaire. If there is no such person in the household, any adult household member 15 years old and over could be designated as the householder.
Households are classified by type according to the sex of the householder and the presence of relatives. Two types of householders are distinguished: a family householder and a nonfamily householder. A family householder is a householder living with one or more individuals related to him or her by birth, marriage, or adoption. The householder and all people in the household related to him or her are family members. A nonfamily householder is a householder living alone or with nonrelatives only.

A household includes all the people who occupy a housing unit. (People not living in households are classified as living in group quarters.) A housing unit is a house, an apartment, a mobile home, a group of rooms, or a single room that is occupied (or if vacant, is intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live separately from any other people in the building and which have direct access from the outside of the building or through a common hall. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated people who share living arrangements. In the 2010 Census data products, the count of households or householders equals the count of occupied housing units.

The spouse category includes a person identified as the husband or wife of the householder and who is of the opposite sex. For most of the tables, unless otherwise specified, it does not include same-sex spouses even if a marriage was performed in a state issuing marriage certificates for same-sex couples.