Appeal from the Circuit Court of Lake County. No. 01-CH-894 Honorable David M. Hall, Margaret J. Mullen, and Barbara Gilleran Johnson, Judges, Presiding.
 The opinion of the court was delivered by: Justice McLAREN
 The State, represented by Lake County State's Attorney Michael J. Waller and then Attorney General James E. Ryan, filed a complaint against defendant, J. Harrison, as trustee under trust No. 410, alleging that he violated various provisions of the Illinois Environmental Protection Act (the Act) (415 ILCS 5/5 et seq. (West 2000)) and the administrative regulations of the Pollution Control Board (35 Ill. Adm. Code §§807, 810, 848 (2000)). After several attempts at personal service failed, the State sought and received the court's permission to serve defendant by publication. Defendant did not appear and the court entered a default judgment. Defendant then appeared and moved to vacate the judgment. The court denied the motion. Defendant appeals, contending that the State did not comply with the requirements for alternative service by special order of the court or for service by publication because the affidavit accompanying the motion was insufficient. Defendant also contends that service by publication is available only in in rem actions while the fine that the court imposed is a personal judgment against him. Because the trial court's determination that the State complied with the requirements for service by special order of the court was not clearly erroneous, we affirm.
 The State's complaint alleged that defendant, as trustee, owned property at 38101 N. Sheridan Road in Beach Park. The property, which appeared to be abandoned, contained tires, drums of petroleum products, and other waste in violation of the Act and regulations promulgated under it.
 The State made several attempts to serve defendant personally or by abode service. The original summons, directed to an address in Mundelein, was returned unserved. An alias summons directed to an address in Tower Lakes was similarly returned unserved. A third alias summons directed to defendant at the Lake County courthouse also was not served. An attempt to serve defendant at an address in Cedar Grove, Wisconsin, was also unsuccessful.
 The State then filed a motion for an order authorizing alternative service. The motion does not state specifically which section of the Code of Civil Procedure (the Code) (735 ILCS 5/1--101 et seq. (West 2000)) it invokes. The motion alleges that "The Plaintiff has made diligent inquiry as to the location of the Defendant, and reasonable efforts to make service have been unsuccessful."
 Attached to the motion was the affidavit of Assistant State's Attorney Lisle Stalter, which alleged the following. Stalter reviewed records in the Lake County recorder's office to learn who purchased the property. This information provided her with a post office box in Mundelein, which she traced to a street address. A Lake County sheriff's deputy attempted to serve defendant at that address, but returned the summons unserved. A colleague then gave Stalter an address for defendant in Cedar Grove, Wisconsin. However, an attempt at service at that address was returned unserved. She found another address in Tower Lakes/Barrington at which to serve defendant. However, the summons was returned unserved as no such address existed. Stalter averred that, "Although a diligent effort has been made, no other information has been found as to where J. Harrison can be personally served."
 The trial court issued an order stating that "Plaintiff's Motion for service by publication is granted as Plaintiff has shown due diligence in attempting to obtain personal service." The court also ordered that defendant be served by regular mail. Later, Stalter filed a second affidavit that was essentially the same as the first, but included the specific addresses at which service was attempted. The State provided publication notice and also mailed copies of the complaint to the addresses at which it had attempted service. Only the envelope sent to the Tower Lakes address was returned.
 Defendant did not appear and the trial court entered a default judgment. It enjoined defendant from future violations of the Act, ordered him to clean up the site, and fined him $79,000. Defendant then appeared and moved to quash the service and vacate the judgment. The trial court denied the motion and defendant timely appeals.
 The parties assert that the standard of review of whether the trial court had personal jurisdiction over defendant is de novo. Although numerous recent cases contain this statement of the standard of review (see, e.g., White v. Ratcliffe, 285 Ill. App. 3d 758, 764 (1996)), it is not necessarily correct. Rather, as in other cases, the appropriate standard depends on how the trial court decided the issue. We note that White cites State Bank v. Thill, 113 Ill. 2d 294, 308-09 (1986), for the proposition that whether the trial court obtained personal jurisdiction over the defendant should be reviewed de novo. Although Thill does not explicitly state a standard of review, the issue there was a legal one, so de novo review was appropriate. However, Thill does not state a general rule that anytime personal jurisdiction is at issue, the standard of review is de novo.
 In Gaidar v. Tippecanoe Distribution Service, Inc., 299 Ill. App. 3d 1034 (1998), the court held that the "manifest weight of the evidence" standard of review applied to jurisdictional issues where the trial court heard courtroom testimony, but that a de novo standard applied when the trial court heard no testimony but decided the jurisdictional issue solely on the basis of documentary evidence. Gaidar, 299 Ill. App. 3d at 1039-40; see also Spartan Motors, Inc. v. Lube Power, Inc., 337 Ill. App. 3d 556, 559-60 (2003). We agree with this analysis to a point. Although in Gaidar and Spartan Motors the issue was whether the defendants were doing business in Illinois for purposes of the long-arm jurisdiction statute (735 ILCS 5/2-209 (West 2000)) rather than whether the defendants were properly served with the summons, this distinction is irrelevant. The critical fact is whether the trial court heard disputed evidence and made factual findings, rather than the substantive issue that the court considered. Here, the court made such findings, and the issue was a mixed question of law and fact. Therefore, we apply the clearly erroneous standard of review.
 "This court reviews pure questions of law under a de novo standard of review, without deference to the circuit court concerning the content of any rule of law relevant to this proceeding. [Citation.] The circuit court's finding of fact, however, is entitled to deference by this court and may be reversed only if it is contrary to the manifest weight of the evidence. [Citation.] Mixed questions of fact and law, which involve the application of law to a particular set of facts, are subject to review under the clearly erroneous standard, affording the circuit court less deference than for questions of fact. [Citation.] Under the clearly erroneous standard of review, a finding by the trial court may be reversed only if, after careful examination of the record in light of the applicable rule of law, the reviewing court is left with the 'definite and firm conviction' that the finding is in error. [Citation.]" Zebra Technologies Corp. v. Topinka, 344 Ill. App. 3d 474, 480-81 (2003).
 Defendant first claims that the trial court did not acquire jurisdiction over him because the State did not comply with the statute authorizing substituted service. If a party is not properly served with a summons, the court has no personal jurisdiction over him or her and any judgment entered against that party is void. Mugavero v. Kenzler, 317 Ill. App. 3d 162, 164 (2000).
 Generally, the Code requires that an individual defendant be served either in person or by abode service--by leaving a copy of the summons with a family member above the age of 13. 735 ILCS 5/2--203(a)(1), (a)(2) (West 2000). However, section 2--203.1 of the Code provides that if service upon an individual defendant is impractical, a plaintiff may request that the court allow "a comparable method of service." 735 ILCS 5/2--203.1 (West 2000). The motion must be accompanied by an affidavit
 "stating the nature and extent of the investigation made to determine the whereabouts of the defendant and the reasons why service is impractical under items (1) and (2) of subsection (a) of Section 2--203, including a specific statement showing that a diligent inquiry as to the location of the individual defendant was made and ...