Preschool attendance not only benefits the later learning of an individual and her subsequent income, it provides external benefits to society in the form of skill spillovers, education peer effects, reduced crime, and less government welfare spending/greater government tax revenue.  Concern has accordingly arisen that the United States lags behind other developed countries in preschool attendance.  This deficit is not consistent across all types of children and locations.  To understand why, this paper offers a regression analysis of what influences the preschool attendance of three-, four-, and five-year olds from a supply and demand perspective using data from the California Health Interview Survey.  The discovery of a positive influence of nearby available preschool slots per those that could possibly attend (supply) on the likelihood of preschool attendance that is greater in magnitude to influences detected for differences in parent education or income (demand), suggests the desirability of further pursuing public policies intended to increase the supply.