The rise in the proportion of single persons living alone in the United States over the last several decades has been explained in two ways. A consumer demand explanation suggests that increases in income and the ability of persons to afford the desired privacy and autonomy of single person households account for the rise. An alternative explanation suggests that norms, residence rules, and tastes have become more supportive of nonfamilial living arrangements in post-industrial societies and that the proportion of persons living alone would have increased substantially even if income had not risen. Previous evidence for these explanations comes from cross-sectional or aggregate data; this paper tests alternative predictions of the explanations using individual-level survey data from three time points—1960, 1970, and 1976. In contrast to predictions of the consumer demand explanation, the results show that major increases in the proportion of single persons living alone are unexplained by increases in income and other individual-level characteristics of respondents. Although the effect of income on living alone has been constant over time, the existence of significant additive effects of time is consistent with alternative explanations of structural changes in propensity to live alone.