In this paper, we conceptualize and develop an index of sociodemographic risk that we hypothesize will be an improvement over the standard poverty measure as a measure of risk for children's development. The poverty line is widely used in government statistics and in research but is also widely acknowledged to have multiple shortcomings. Using recent data from the National Survey of America's Families, we develop and examine a Sociodemographic Risk Index for two potential purposes: (a) to serve as a summary indicator of children's environments that affect their well-being, and (b) to serve as a variable that can be used to identify at-risk subgroups of children whose well-being should be examined separately in indicator reports. Based on substantial research on children's development, we chose five variables for the index: family income, family structure, parent education, family size, and home ownership. An additive sociodemographic risk index using these variables is strongly associated with multiple measures of child well-being in both bivariate and multivariate analyses. Hence, it serves as a good marker of risk for children and therefore as an indicator that could be monitored over time, across groups, and across places, as well as a variable that could be used to identify subgroups of at-risk children whose well-being should be monitored. However, analyses do not indicate that it performs better at identifying at-risk children than the current poverty measure. Therefore, we recommend the Sociodemographic Risk Index primarily as an additional summary indicator to be monitored, rather than as a replacement for the poverty measure.