The top five most common family names in the United States in order include "Smith," "Johnson," "Williams," "Jones" and "Brown," according to About.com. Other common family names listed in the top 100 list by About.com are "Miller," "Davis," "Garcia," "Wilson," and "Rodriguez." Some of these names have an English, Scottish, Spanish, Irish or Italian origin. Other common family names have a French, German or Welsh origin.
There are over 2 million people with "Smith" as their family name. The occurrence of Smith per 100,000 people is 880, while that of "Miller" is 418 people per 100,000 population. "Smith" is an English name, while "Rodriguez" is a Spanish name. While "Smith" is common among 73.35 percent of non-Hispanic whites and 1.56 percent of Hispanics in the United States, "Rodriguez" is common among 92.7 percent of Hispanics and 5.52 percent of non-Hispanic whites in the United States, as MongaBay.com reports.
Some countries have laws that require their citizens to have a family name, as Wikipedia notes. Most cultures in the world use family names, but the process of choosing or using the names may differ. In most cases, families pass on the name of the father to the child, but a child may use the mother's family name in the case of single mother parenthood. Women may also adopt the family name of their husbands once they get married.