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Heyl Royster



Mark McClenathan (Shareholder)


Mark concentrates his practice in commercial and civil litigation. He has extensively defended product liability, professional and construction liability, trucking, and agriculture liability cases. He is chair of the firm's Construction Practice.

Mark has handled cases in state courts in more than 19 counties in northern Illinois, including Cook County, and in federal court in the Northern District of Illinois. He has successfully tried numerous high-exposure construction, trucking, and product liability cases to verdict. In October 2012, Mark obtained a defense verdict for a trucking company in a wrongful death lawsuit in LaSalle County, IL where the plaintiff claimed violations of numerous federal and state trucking regulations. He is licensed to practice in Illinois and Iowa.

Mark has an extensive background in building construction and mechanics. Mark has also successfully defended product liability cases involving construction equipment, automobiles and trucks, industrial equipment and machine tools, and hunting products. Mark has represented manufacturers and retailers of ladders, cranes, machine tools, engines, fuel systems (in semi- tractor trucks and luxury yachts), deer hunting stands, electrical systems and equipment, food manufacturing equipment, amusement park attractions, building materials, and lawnmowers. He has represented numerous general and subcontractors in building, civil and road projects.  As part of his professional liability practice, Mark has defended engineers, architects, agents and brokers, and real estate appraisers.

Mark has successfully defended farmers, farm service companies and co-ops, and grain storage facilities.  Mark has recently defended cases involving chemical spills and spray drift/off target claims, crop and nursery damage claims, farm equipment accidents, and grain bin fatalities.

In addition, Mark has represented clients in the areas of business and corporate law, construction law, and real estate. Also, Mark has represented municipalities and clients before various governmental bodies, and has experience in annexations, subdivisions and developments, zoning, and intergovernmental agreements.

Mark joined Heyl Royster in 1989, and became a partner with the firm in 1998. Prior to joining Heyl Royster, Mark worked for the legal department of the Defense Logistics Agency (Defense Contract Services) of the Department of Defense in Chicago; the legal departments of Land O'Lakes, Inc. in St. Paul and 3M Corporation in Minneapolis.

Significant Cases

  • Represented a restaurant and bar at trial in a wrongful death lawsuit in Winnebago County, IL involving the shooting of the plaintiff decedent. Obtained summary judgment on the Dram Shop counts before trial, and obtained a defense verdict on the remaining negligence counts at trial.
  • Represented a trucking company at trial in a wrongful death lawsuit in LaSalle County, IL where the plaintiff claimed violations of numerous federal and state trucking regulations. At trial, Mark obtained a defense verdict.
  • Defended and obtained dismissal of a federal lawsuit filed against the designer and builder of an ethanol plant in which the owner claimed lost income and production resulting from several fires at the plant.
  • Represented civil engineers and highway construction contractors in defense of complex claims relating to road construction design, construction supervision,  and alleged road defects (such as failed concrete, pavement markings, construction signage), leading to personal injuries and wrongful death claims. Mark obtained dismissal of all claims.
  • Defended a complex claim, including claims for injunctive relief and breach of contract, brought by an Illinois municipality against its cable franchisee for alleged violations of a Franchise Agreement, including litigation over the interpretation of the amended Illinois Cable and Video Customer Protection Law, 220 ILCS 5/22-501(b)(3) and related municipal regulations.
  • Defended and obtained dismissal of a federal claim against a farm service for negligently spraying a farmer's corn crop with a herbicide in violation of federal statues, rules and regulations, and allegedly destroying his corn crop.
  • Defended and obtained dismissal of two separate preferential treatment claims in the U.S. Bankruptcy Court against creditors of companies filing for bankruptcy, and successfully prosecuted a Section 523 Complaint to Determine the Dischargeability of a Debt in a construction case.


  • Assisted various municipalities on incorporations; drafting new or amending existing zoning, subdivision, and general ordinances; drafting comprehensive plans; negotiating and drafting border agreements and annexation agreements.
  • Represented municipalities in court on border disputes.
  • Represented municipalities before administrative boards on disciplinary proceedings (including police issues).
  • Represented Ken Rock Community Center on sale of commercial/school property.


  • “Crossing the Line: Interference with Business and Contractual Relations,” Illinois Defense Counsel Quarterly Monograph (2017) - Download Article
  • "Proposed Law Would Not Allow Counties to Set Standards for Wind-Farms," Heyl Royster Governmental Practice Client Alert (2014) - Read Article
  • "Sale of Goods - Disclaiming of Warranties and Consequential Damages," Heyl Royster Business & Commercial Litigation Newsletter (2014) - Read Article
  • "Municipal Bankruptcy - Can an Illinois Municipality File for Bankruptcy Protection?," Heyl Royster Governmental Newsletter (2014) - Read Article
  • "Protect Your Business - The Three Component Test For Restrictive Covenants In Employment Contracts," Heyl Royster Business & Commercial Litigation Newsletter (2013) - Read Article
  • "The Effect of The Illinois Firearm Concealed Carry Act on Municipalities" (2013) - Download Article

Public Speaking

  • “Risk Transfer in Contracts ‘Key Provisions and Remedies You Must Have’”
    Heyl Royster “Avoiding Litigation Part Deux” Seminar 2018
  • “Liability Protection: ‘How to Prevent the Piercing of the Corporate Veil’”
    Heyl Royster “Avoiding Litigation Part Deux” Seminar 2018
  • “CyberLiability for Park Districts: How to Build Your Defenses for a Cyber Attack”
    IAPD and IPRA Soaring to New Heights Annual Conference 2018
  • “Cyber Liability”
    Heyl Royster Governmental Seminar 2017
  • “Best Practices for Minimizing Cyber Liability”
    Illinois Association of Park Districts Legal Symposium 2017
  • “We Need a New Stadium – If You Build It, Suits Will Come: Construction Coverage Issues”
    Heyl Royster's 32nd Annual Claims Handling Seminar 2017
  • “Get Organized”
    Heyl Royster Governmental Seminar 2016
  • “Liability Protection: How to Prevent the Piercing of the Corporate Veil”
    Northern Illinois Builders Contractors Association (NIBCA) 2016
  • “Preserving Electronic Information: Protect your business in the event of a lawsuit or the threat of a lawsuit.”
    Heyl Royster “Avoiding Litigation” Seminar (Urbana, IL) 2016
  • “Staying Out of Litigation: When to Require Liability Waivers”
    IAPD/IPRA "Soaring to New Heights" Conference 2016
  • Click here to view full list”

Professional Recognition

  • Selected as a Leading Lawyer in Illinois. Only five percent of lawyers in the state are named as Leading Lawyers
  • Winnebago County Pro Bono Volunteer of the Year (1990)
  • Court certified mediator, Winnebago County
  • Meritorious Service Award by the Illinois Association of Defense Trial Counsel

Professional Associations

  • Winnebago County Bar Association
  • Illinois State Bar Association
  • Illinois Association of Defense Trial Counsel (Board of Directors, 2018-present; Chair, Commercial Law Committee 2016-2017; former Chair, Construction Law Committee 2015-2016)
  • Defense Research Institute 

Court Admissions

  • State Courts of Illinois
  • State Courts of Iowa
  • United States District Court, Northern District of Illinois

Community Involvement

  • Wesley Willows – Chairman of the Board (Rockford's largest and only accredited continuing senior care retirement community in Rockford)
  • Boy Scout leader – Troop 620 (Roscoe, IL), and Eagle Scout Board of Review (Glacier's Edge Council in South Central Wisconsin and Northern Illinois). Merit badge counselor, Eagle Scout candidate mentor. Past Board of Review Chair; Campmaster, high adventure; Assisted special construction projects and Eagle Scout projects.
  • Private Pilot – Member of AOPA, EAA
  • Beloit Rifle Club – Volunteer: Special Building Projects; Grounds; Matches; and gun training/sight in shoots
  • Civilian rifle instructor – Annual Armed Forces Camp (AFC) in Wisconsin to train Marine Poolees.
  • Active member in Antique Automobile Club of America (AACA) and other antique car clubs
  • Former High School Coach – 8-year High School (certified) girls' fast pitch softball coach
  • Boys and Girls Club – Former baseball coach and Special Building Projects Leader
  • Club Sports – Former General Manager, coach and assistant coach of various youth travel baseball and softball teams
  • YMCA (Stateline) – Former member of the Special Building Committee, and volunteer basketball and football coach
  • Roscoe Youth Baseball Association – Former coach, baseball commissioner, tournament director and special projects coordinator (parks, buildings, and diamonds)
  • Harlem Community Center – Former basketball coach
  • Swim meet official – (timer, announcer)
  • Lecturer – Multiple high schools, not-for-profit organizations, clubs
  • Active supporter of many other local charities and not-for-profit groups