Using data from Illinois, I examine relationships between the number of private schools and characteristics of the public schools and surrounding population. I find positive, statistically significant relationships between number of private schools in 1998 and public school 3rd grade class size, the percent college educated, and the percent over 55 years of age. I find significant negative relationships between number of private schools and average household income and racial concentration. Looking at private school entry, areas with larger increases in the school-aged population had less entry, and areas with increasing income dispersion experienced greater entry. The results suggest that if a universal education voucher program is introduced, parents in relatively well-educated, racially diverse, and more moderate income areas will likely have greater access to private school options because of more existing private schools in their area. These areas will also likely have more private school entry in response.