Not necessarily. In Illinois civil procedure, if a complaint is "verified" (meaning the plaintiff swears to the truth of the facts asserted, much like an affidavit) then the court will construe it to be evidence unless opposed by the defendant. Now, if a defendant shows up to trial and wants to cross-examine the claims made in a verified complaint (and a defendant has a near-absolute right to cross-examination in Illinois) and the Plaintiff is not present, the court will likely continue the matter and require the plaintiff to appear.
Alternatively, if you have evidence to rebut the claims (as opposed to attacking the claims themselves) a court MAY weigh the verified claims against your evidence. However, they most likely will continue to require the plaintiff to appear.
Defendants also have a procedure for making parties (such as the plaintiff) appear at trial personally for examination purposes. This is contained in the Supreme Court rules and the mechanics of doing so can be learned at the pro se help desk down at the Daley Center. They will also be able to examine the complaint and tell you whether it is "verified" or not.
NOTE: This answer is not intended to be legal advice and should not be construed in that way. This answer does not create an attorney-client relationship and no such relationship may be created absent a signed retainer agreement. The author is licensed in Illinois only, and his answer is for educational purposes alone.