Any voucher program that is going to have a major impact on a public education system is likely to require an expansion of private schools in order to accommodate increased demand; however, little is known about where private schools open and therefore how a major voucher program might affect private school availability in various communities. Using data from Illinois, the author examines the relationship between the number of private schools in a zip code and the characteristics of the public schools and population of the zip code. Significant positive relationships are reported between the number of private schools in 1998 and average 3rd grade class size in the public schools, the percent of the population that is college educated and the percent of persons over 55 years of age. In addition, significant negative relationships are reported between the number of private schools and average household income of the community and an index of racial concentration. Relationships between private school location and neighborhood characteristics were also investigated. Results indicated that community homogeneity is associated with less demand for private schools, suggesting that children living in more heterogeneous neighborhoods may be more likely to have private school access and to get more private school entry under a universal voucher program. (Contains 3 footnotes, 3 figures and 9 tables.)