Validating the structure of informal numeracy skills is critical to understanding the developmental trajectories of mathematics skills at early ages; however, little research has been devoted to construct evaluation of the Numbering, Relations, and Arithmetic Operations domains. This study was designed to address this knowledge gap by examining the structure of these three numeracy skill domains and examining the relations among these domains. Three hundred ninety-three children participated in the study (51.7% girls, 55.7% White, 33.8% African American, and 10.5% other). Results indicated that the relations among the informal numeracy skills were best explained by a three-factor model that included Numbering, Relations, and Arithmetic Operations factors, and this factor structure was the same in both younger and older preschool children. (Contains 9 tables, 1 figure, and 5 notes.)