How many undocumented students do we have?

There is no exact number available.   

According to assistant principal Dr.Parrie, under federal guidance, K-12 public schools cannot ask about child’s immigration status and, even if they do know, staff must treat them no differently than U.S. citizen students. …While schools must protect the rights and privacy of students, officials also must cooperate with federal officials in some instances”.  

According to Wikipedia, in the nation we have 11.1 million undocumented immigrants. According to Migration Policy Institute, in Illinois we have around 487,000 immigrants and majority of the population are from Mexico with 64% (311,000). From birth to 24 years there is a total of 96,000 immigrants.