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About McMahon Law Offices

Two Sides.
One Courthouse.
One Mission.

McMahon Law Offices defends criminal charges in DuPage County. Our team includes a former prosecutor who built cases in this courthouse and a retired judge who decided them. The judges, the prosecutors, the clerks. We know them all.

40+ Years
Combined Criminal Defense Experience
18th Circuit
Our Home Courthouse
2 Perspectives
Former Prosecutor + Retired Judge
1 County
DuPage. We Go Deep, Not Wide.
MLO

"DuPage County defendants deserve counsel who knows this courthouse, not an attorney who learns it on their behalf. We have been in this courthouse every day of our careers."

01 — Overview

DuPage County's Insider Defense Firm

McMahon Law Offices defends criminal charges in DuPage County. We do not practice across every county in Illinois. We practice here, in front of the same judges, working with the same prosecutors, inside the same courthouse our clients' cases will be heard in.

Our team includes a former DuPage County prosecutor and a retired 18th Circuit judge. That combination is not common. It means we understand the case from every angle before we walk into the courtroom.

40+ Yrs
Combined Criminal Defense Experience
2
Inside Perspectives — Prosecutor + Judge

02 — Our Story

Built From Inside the Courthouse

Mike McMahon started as a prosecutor in the DuPage County State's Attorney's Office. He tried DUI cases, drug charges, violent crimes, and felonies before the judges of the 18th Circuit. He founded McMahon Law Offices to bring that insider knowledge to the defense side.

The decision was deliberate. He had seen firsthand that knowing which arguments worked with which judges, and where the state's cases had procedural weaknesses, produced better outcomes. That knowledge only belongs to attorneys who practice in DuPage County every single day.

"DuPage County defendants deserve counsel who knows this courthouse, not an attorney who learns it on their behalf."

  • Mike McMahon admitted to the Illinois Bar in 1975
  • Served as Assistant State's Attorney, DuPage County
  • Founded McMahon Law Offices to bring prosecution experience to the defense side
  • Judge Cary B. Pierce joined after retiring from the DuPage County bench
  • 40+ years of combined practice before every judge on the 18th Circuit

03 — Our Approach

How We Handle Every Case

We start with dismissal. Not damage control. We look for the weakest element of the state's case before any negotiation begins. Was the stop legal? Was the evidence obtained properly? Were required procedures followed? Only after that examination do we consider outcomes beyond dismissal.

  • Immediate evidence review. We pull police reports, dashcam footage, and lab results from day one.
  • Suppression motions first. If the evidence was obtained improperly, it goes away. When the evidence goes, the case often follows.
  • Prosecutor relationships. Mike knows the DuPage County SA's office from the inside. That changes how negotiations go.
  • Judge-specific strategy. Every judge has tendencies. We know them. We build arguments accordingly.
  • Honest case assessment. We tell you what is realistic, not what sounds good. No promises we cannot keep.

04 — Philosophy

The Permanent Record Is the Real Penalty

The fine is paid once. Probation ends. But a criminal conviction in Illinois follows you into every background check, every job application, and every professional license renewal for the rest of your life. Many charges, including DUI, cannot be expunged.

That single fact shapes how we defend every case. We fight hard because the stakes are permanent, even when the charge seems minor.

  • A conviction is forever. The fine is temporary.
  • Many Illinois charges, including DUI, are not expungeable.
  • Background checks affect employment, housing, and professional licensing for life.
  • The right outcome now protects every opportunity you have ahead.

05 — Why McMahon

What No Other DuPage Firm Can Offer

Most defense attorneys learned the 18th Circuit by practicing in front of it. We learned it from two additional angles: as the prosecutor building cases, and as the judge deciding them. That is not a marketing claim. It is the actual background our attorneys bring to your case.

  • Former prosecutor on your team. Mike McMahon knows how the DuPage County SA's office builds cases and where they fall apart.
  • Retired judge on your team. Judge Pierce knows what arguments resonate with every judge in Wheaton and how cases look from the bench.
  • 40+ years of daily presence. We know the clerks, the prosecutors, and the judges. Not from research. From showing up every day for four decades.
  • No out-of-county learning curve. This is not a market we serve. It is where we work.
  • Single courthouse focus. We go deep, not wide. Our expertise in DuPage County is unmatched because we have never diluted it.

06 — The Attorneys

Two Perspectives. One Firm.

McMahon Law Offices is built around a simple idea: the attorneys who understand how cases are built and decided will defend them better than attorneys who only know one side. Our team has sat at the prosecution table, on the bench, and at the defense table. Your case benefits from all three.

  • Michael F. McMahon — Former DuPage County prosecutor. Has defended thousands of criminal cases before the 18th Circuit over a career spanning more than four decades.
  • Judge Cary B. Pierce (Ret.) — Retired Circuit Judge, 18th Judicial Circuit. Presided over criminal cases at the DuPage County Courthouse in Wheaton. Knows every judge on the current bench personally.

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