Sara Tonnies Horton
Partner, Litigation
Sara Tonnies Horton is Co-Chair of the IP Litigation Practice Group and focuses her practice on complex civil and intellectual property litigation in courts around the country, particularly patent and technology-related litigation matters. Sara has demonstrated first chair trial skills in scores of patent litigation matters and has tried several high-stakes trials in recent years. She has represented clients in disputes involving a variety of technologies including pharmaceuticals, polymers, packaging, alloys, and food manufacturing. In addition to patent matters, Sara has tried antitrust, actuarial malpractice, anti-dumping and transshipment, and other types of cases to juries. Sara has experience before the PTAB and currently serves as co-chair of the Amicus Committee of the PTAB Bar Association.
Chambers USA consistently recognizes Sara as among the leading practitioners in the area of Intellectual Property. In its 2025 edition, one client reported to Chambers that "Sara is one of the finest patent litigators with whom I have worked. She is a top-notch first chair litigator." Another client previously reported to Chambers that "Sara's acumen in the courtroom well outpaces that of opposing counsel time and time again. Sara is an in-house counsel's dream – she is exceptional at framing complex legal matters in an easy to decipher manner." Sara is also recognized by leading national outlets, including IAM Patent 100, The Legal 500 Patent Litigation and Managing IP, among others.
Sara is a member of the Children’s Research Fund's Board of Directors. In addition, Sara teaches trial advocacy at the Harvard Law School and is an active member of the Richard Linn American Inn of Court.
Experience
Sara was previously an equity partner at another major law firm in Chicago.
- The Legal 500 United States – Dispute Resolution - General Commercial Disputes (2025)
- Lawdragon, 500 Leading Global IP Lawyers (2025)
- Chicago Daily Law Bulletin/Chicago Lawyer, "5th Annual Top Women in Law" (2024)
- Benchmark Litigation – Litigation Star (since 2024)
- Euromoney Women in Business Law – Patent Lawyer of the Year, Shortlist (2024)
- Managing IP
- Illinois Litigator of the Year, Shortlist (since 2024)
- Patent Star: Illinois (since 2024)
- Top 250 Women in IP (2025)
- Chambers USA – Intellectual Property in Illinois (since 2021)
- Lawdragon 500 Leading Litigators in America (since 2024)
- The Legal 500 United States – Intellectual property, Patents: litigation (since 2023)
- DePaul University College of Law’s Via Sapientiae Award for outstanding contributions to the university (2022)
- Crain’s Chicago Business' Notable Women in Law (2022)
- IAM Patent 1000 (since 2022)
- Irish Legal 100 (since 2023)
- Illinois Super Lawyers - Illinois Property Litigation (since 2024)
- Chicago Daily Law Bulletin "40 Under Forty" (2019)
- Law Bulletin Publishing Company - Leading Lawyers Network "Emerging Lawyer," Commercial Litigation; Intellectual Property Law (2015-2019)
- Best Lawyers in America
Litigation – Intellectual Property (since 2023)
Patent Law (since 2023)
Publications
- Co-Author, “SIPCO and Covered Business Methods – Courts Continue to Struggle with PTAB Regs,” Bloomberg Law, November 15, 2019
- “Supreme Court Upholds, and Changes, IPR Administrative Patent Challenges in Oil States and SAS,” April 25, 2018
Speaking Engagements
- Speaker, Harvard Law School Winter 2024 Trial Advocacy Workshop, January 2024
- Panelist, "Learn About the PTAB Judicial Law Clerk Program," United States Patent and Trademark Office, August 19, 2021
- Panelist, "Stopping at the PTAB - The Estoppel Effect of PTAB Decisions," The Power of PTAB: The New Authority in Patent Law, October 20, 2017
- PTAB Bar Association Inaugural Conference, March 1, 2017 to March 3, 2017
- "The Strategy of District Court Litigation vs. IPR in View of Recent Appellate Decisions," IP Strategy Summit, October 13, 2015
- University of Chicago Law School Intellectual Property Law Society, February 11, 2015
Sara has significant trial experience, trying more than 10 cases to juries and judges in various Federal and State courts*:
- Representation of generic pharmaceutical company in ANDA litigation in the District of Delaware related to a sedative. The district court ruled in favor of our client and the Federal Circuit affirmed (en banc).
- Defended an industrial and farming equipment manufacturer in a patent infringement matter in the Southern District of Iowa. Secured a complete victory for the client after a 3 week jury trial. The Federal Circuit affirmed on all issues.
- Successful representation of a global chemical manufacturer in a federal jury trial in Nevada in connection with multimillion-dollar claims arising out of equipment breakdowns at a chemical manufacturing facility.
- Enforced patents for branded pharmaceutical client in ANDA litigation in the District of Delaware, judgement affirmed on appeal.
- Represented a pro bono client in defense of murder charges in a two week jury trial in Illinois. During that trial, she handled direct and cross examinations of various forensic witnesses.
- Successfully enforced patents related to ethylene polymer films and obtained a $61.7 million jury verdict for a major chemical company in the District of Delaware. The Federal Circuit affirmed this verdict on appeal.
- Successful defense of a client against a $40 million patent infringement and tortious interference suit in the District Court for the District of Delaware.
- Representation of branded pharmaceutical company in ANDA litigation in the Southern District of New York.
* Sara advised on these matters prior to joining Willkie.
Credentials
Education
DePaul University College of Law, J.D., 2005 University of Notre Dame, B.S., Chemistry, 2002
Bar Admissions
Court Admissions
United States Patent & Trademark Office United States Court of Appeals, Federal Circuit United States District Court, Northern District of Illinois (Trial Bar) United States District Court, Western District of Wisconsin United States Court of Appeals, 9th Circuit United States Court of International Trade United States Court of Appeals, 7th Circuit