Justices Freeman, Thomas, Kilbride, Karmeier, Burke, and Theis concurred in the judgment and opinion.
GARMAN, CHIEF JUSTICE
¶ 1 This case concerns the proper situs for tax liability under retail occupation taxes arising under three Illinois statutes: the Home Rule County Retailers' Occupation Tax Law, the Home Rule Municipal Retailers' Occupation Tax Act, and the Regional Transportation Authority Act. The Illinois Department of Revenue determined through audit that plaintiff Hartney Fuel Oil Company's sales at retail were attributable to the company's Forest View office, rather than the Village of Mark location reported by the company. The change in location made Hartney subject to retail occupation taxes imposed by the Village of Forest View, Cook County, and the Regional Transportation Authority. The Department issued a notice of tax liability, which Hartney paid under protest. Hartney then filed for relief in the circuit court of Putnam County.
¶ 2 The circuit court of Putnam County consolidated with this case a declaratory judgment action by the board of commissioners of Putnam County and board of trustees of the Village of Mark, in which those local governments sought to be declared the proper situs of taxation. The circuit court also allowed the board of trustees of the Village of Forest View, the County of Cook, and the Regional Transportation Authority to intervene as defendants. The circuit court, interpreting the Department of Revenue's regulations for the three taxes, found for the plaintiffs. The appellate court affirmed that decision. 2012 IL App (3d) 110144.
¶ 3 We granted defendants' petitions for leave to appeal pursuant to Supreme Court Rule 315 (eff. Feb. 26, 2010). Pursuant to Supreme Court Rule 345 (eff. Sept. 20, 2010), we have permitted the Taxpayers' Federation of Illinois and the Illinois Retail Merchants Association to file a brief amicus curiae on behalf of the plaintiffs. We have also permitted the Village of Schaumburg, the City of Chicago, the City of Peoria, the Town of Normal, and the County of Peoria to file a brief amicus curiae on behalf of the defendants.
¶ 4 BACKGROUND
¶ 5 Hartney Fuel Oil Company is a retailer of fuel oil, and during all times relevant to this litigation its home office was in Forest View, Illinois. From its Forest View office, Hartney would set fuel prices, cultivate customer relationships, and handle administrative tasks like billing and accounting. Each night, Hartney staff there would communicate fuel prices for the following day to prospective customers. The Forest View home office also contained a jointly owned but separately incorporated transportation company, Energy Transport, Inc. Energy Transport served as a common carrier, filling many of Hartney's fuel orders.
¶ 6 In addition to its Forest View office, Hartney had a "sales" office, located elsewhere in the state for tax planning purposes. The sales office had no direct employee of Hartney; Hartney would contract with a local business for a clerk to take fuel orders. Hartney established its first separate sales office in Elmhurst, later moving it to Burr Ridge, then to Peru, and then to Mark, due to prevailing local tax conditions. The local business would provide the services of one of its own employees to receive Hartney's orders via phone; Hartney would pay the local business a flat rate. During the relevant time period, Hartney paid Putnam County Painting, a commercial painting business, $1, 000 per month for a nonexclusive lease of 200 square feet and the services of a clerk.
¶ 7 Hartney had two varieties of fuel contracts, long-term requirements contracts and daily orders. Customers would call the Mark office to place their daily orders. Any customer who called the Forest View office to place an order was directed to call the Mark office. The clerk in Mark would check a list of customers with approval to order on credit. Orders from those who were not credit-approved would be rejected. For customers who were preapproved, the clerk would call Energy Transport at the Forest View office, and Energy Transport would deliver the fuel. No confirmation of the order by Hartney's Forest View office was required. Testimony at trial and the conclusion of the circuit court were that the clerk's word was binding on Hartney.
¶ 8 Long-term requirements contracts were negotiated by Hartney's president, who would instruct the customer to sign the contract and return it by mail to the Mark office. If Hartney's president had not yet signed the contract, he would travel to the Mark office to sign it. The executed contracts were stored at the Mark office, with copies sent to the customer and Hartney's Forest View office. These contracts were generally on a "keep full" basis. Energy Transport or another common carrier would monitor and keep full the customer's tanks, notifying Hartney to invoice the long-term contract customer for any fuel delivered. The keep-full arrangements did not require any intervention by the Mark office.
¶ 9 By structuring its sales in this way, Hartney hoped to avoid liability for retail occupation taxes of Cook County, the Village of Forest View, and the Regional Transportation Authority. Such taxes are imposed pursuant to the Home Rule County Retailers' Occupation Tax Law (55 ILCS 5/5-1006 (West 2012)), the Home Rule Municipal Retailers' Occupation Tax Act (65 ILCS 5/8-11-1 (West 2012)), and the Regional Transportation Authority Act (70 ILCS 3615/4.03 (West 2012)). Hartney's interpretation of the law was that the relevant regulations set a bright-line test: where the purchase order is accepted for a sale at retail in Illinois, and the purchaser takes delivery in Illinois, the sale has its situs where the seller accepts the purchase order. This view of the situs of sale also meant that Putnam County and the Village of Mark received the portions of the Illinois Retailers' Occupation Tax funds designated for county and local government.35 ILCS 120/3 (West 2012).
¶ 10 The Department of Revenue audited Hartney's selling activity from January 1, 2005, to June 30, 2007, finding the proper situs of selling activity to be Hartney's office in Forest View. The Department calculated retail occupational taxes of Cook County, Forest View, and the Regional Transportation Authority, and sent Hartney a notice of tax liability on September 5, 2008. With interest and penalties, Hartney owed $23, 111, 939.11.
¶ 11 Hartney paid the assessment and sued for a refund under the State Officers and Employees Money Disposition Act (Protest Monies Act) (30 ILCS 230/1 et seq. (West 2008)) in Putnam County circuit court. Putnam County and the Village of Mark joined Hartney in seeking declaratory and injunctive relief to find Mark to be the proper situs of sale, to release the state occupation tax money to Mark and Putnam County, and to release to Hartney the money it paid under protest. Forest View, Cook County, and the Regional Transportation Authority (Local Governments) intervened as defendants.
¶ 12 The circuit court concluded that Hartney had accepted both its long-term sales and daily order sales in the Village of Mark, and that the regulations relevant to each section established a bright-line test for situs of sale: where purchase orders are accepted, tax liability is incurred. The appellate court affirmed.
¶ 13 ANALYSIS
¶ 14 The issues presented by this appeal are (1) the legislative intent of the retail occupation tax statutes, and (2) interpretation of the administrative regulations implementing the retail occupation taxes.
¶ 15 Hartney argues, and the courts below found, that the plain language of the regulation establishes a bright-line test for the situs of retail occupation tax liability. The Department argues that such an interpretation is at odds with this court's decisions on the business of selling under the retail occupation tax and with the legislative intent of the Home Rule County Retailers' Occupation Tax Law (55 ILCS 5/5-1006 (West 2012)), the Home Rule Municipal Retailers' Occupation Tax Act (65 ILCS 5/8-11-1 (West 2012)), and the Regional Transportation Authority Act (70 ILCS 3615/4.03 (West 2012)).
¶ 16 This appeal concerns interpretation of statutes and regulations, both questions of law which we review de novo. People ex rel. Madigan v. Illinois Commerce Comm'n, 231 Ill.2d 370, 380 (2008). Yet even where review is de novo, an agency's interpretation of its regulations and enabling statute are "entitled to substantial weight and deference, " given that "agencies make informed judgments on the issues based upon their experience and expertise and serve as an informed source for ascertaining the legislature's intent." Provena Covenant Medical Center v. Department of Revenue, 236 Ill.2d 368, 387 n.9 (2010).
¶ 17 Factual determinations of a trial court are reviewed under the manifest weight of the evidence standard and will be reversed only where the "opposite conclusion is clearly evident or the finding is arbitrary, unreasonable, or not based in evidence." Samour, Inc. v. Board of Election Commissioners, 224 Ill.2d 530, 544 (2007). The parties disagree about the legal significance of a number of facts in issue but do not dispute the facts themselves.
¶ 18 This dispute arises under the Protest Monies Act (30 ILCS 230/1 (West 2008)). A taxpayer willing to pay an assessment under protest may pay assessed taxes and file suit for a refund in circuit court, thereby avoiding the requirement under the Administrative Review Law (735 ILCS 5/3-101 et seq. (West 2008)) to exhaust all administrative remedies before seeking judicial review.
¶ 19 The Local Retail Occupation Tax Acts
¶ 20 The three statutes at issue (the local ROT Acts) allow home rule county and municipal governments and the Regional Transportation Authority (RTA) to impose a retail occupation tax "upon all persons engaged in the business of selling tangible personal property" at retail within the county, municipality, or metropolitan region. 55 ILCS 5/5-1006 (West 2012); 65 ILCS 5/8-11-1 (West 2012); 70 ILCS 3615/4.03(e) (West 2012). The Village of Forest View is within Cook County and within the metropolitan region of the RTA. Each of the Local Governments has imposed its own retail occupation tax.
¶ 21 The local ROT Acts give information about the tax rate to be imposed and types of products subject to the tax, but—with the exception of coal and other mineral extraction—they do not offer substantial guidance on the proper situs of taxation. See, e.g., 55 ILCS 5/5-1106 (West 2012). For guidance on the proper situs of retail occupation tax under the local ROT Acts, one must turn to the regulations. The "Jurisdictional Questions" regulations for the county, municipality, and RTA retail occupation taxes are largely identical, with only minor differences in layout. See 86 Ill. Adm. Code 220.115 (2000); 86 Ill. Adm. Code 270.115 (2000); 86 Ill. Adm. Code 320.115 (2000). For simplicity, we refer to the Home Rule County Retailers' Occupation Tax Law regulations (86 Ill. Adm. Code 220.115 (2000)).
¶ 22 The circuit court and appellate court both found the regulations to establish a bright-line test: "If the purchase order is accepted at the seller's place of business within the county, municipality and/or metropolitan region; ROT liability is fixed in that respective county, municipality and/or metropolitan region." 2012 IL App (3d) 110144, ¶ 53. The Department and Local Governments argue that the regulations instead present a fact-intensive inquiry, looking to the totality of the circumstances. They argue that only a totality-of-the-circumstances view accords with the legislative intent of the local ROT Acts and this court's prior interpretation of the "business of selling" under the local ROT Acts. See, e.g., Ex-Cell-O Corp. v. McKibbin, 383 Ill. 316 (1943).
¶ 23 We look first to interpretation of the statutes, beginning ...