Two or more persons living in same household who are related by blood, marriage, or adoption. (No families are recognized in group quarters. ) All persons living in a household related to each other are regarded as one family. For instance, a son of the head and his wife living in the household are treated as part of the heads family.

The number of families does not necessarily equal the number of households, since not all households include families. Families are classified in the complete-count basic records by family size or number of persons in a family from 2 persons to 35 persons. Average number of persons per family is calculated.

Family whose head is also the household head. In 1970, primary families are simply termed families.

Married couple with or without own children, or one parent with one or more own children (parent-child group), living in a housing unit and related to the household head, but excluding the head (for example, a son, his wife and children, living with the household head). Since subfamily members are counted as part of the heads (primary) family, too, the number of subfamilies is not included in the count of families per seer in any tabulations for families. Census basic records include categories of sub-families by family type.

In 1960, a family in a household whose head was not related to the household head. In 1970, secondary families are not recognized (since there are so few); persons formerly classed as secondary family members are classed as secondary individuals.

Persons not living with relatives, but living in a household entirely alone or with one or more persons not related to him, or living in group quarters (excepting inmates of institutions).

Household head living alone or with nonrelatives only. The number of primary individuals living alone equals the number of one-person households.

Unrelated individual who is not a household head or who lives in group quarters (excepting inmates of institutions).

One person in each household was designated as the head, that is, the person who was reported as the head by the members of the household. However, if a married woman living with her husband was reported as the head, her husband is considered as the head for the purpose of simplifying the tabulations.

Two types of household head are distinguished -- head of a family and primary individual. A family head is a household head living with one or more persons related to him by blood, marriage, or adoption. A primary individual is a household head living alone or with non-relatives only.

A woman married to and living with a household head. This category includes women in common-law marriages as well as women in formal marriages. In complete- count tabulations, the number of wives of head is the same as the number of husband-wife households and the number of husband-wife families. The number does not equal the number of married women, husband present, since it excludes those married women whose husbands are not household heads (as in subfamilies, Concept No. 81.111).

A son, daughter, stepchild, or adopted child of the head of the household of which he is a member, regardless of the child's age or marital status. The category excludes sons-in-law and daughters-in-law. (Also see own children Concept No. 84.1. )

Household member related to head by blood, marriage, or adoption, but not included specifically in another relationship category. In the sample they are classified as grandchild of head, parent of head or son or daughter-in-law of head, brother or sister of head, parent-in-law of heads or brother or sister-in-law of head and other relative of head, and are identified as separate categories in some tabulations.

Any household member not related to the head; further classified as lodger, resident employee, and friend or partner. These categories are recorded as sample items only.

Persons identified as roomer, boarder, lodger. In the sample it includes foster children not already identified as roomer, boarder or lodger.

An employee of the household (such as maid, cook, hired farm hand, companion, nurse), who usually resides in the housing unit. Also includes the employees relatives living in the housing unit.

This is a residual category, including all persons not identified as roomer, boarder, or lodger or resident employee. In tabulations, it is often combined with roomer, boarder, lodger.