Ker v. Illinois was a United States Supreme Court case that addressed the issue of whether a state could deny a defendant the right to a jury trial in a criminal case. The case was brought by a man named John Ker, who was charged with a crime in Illinois. Ker argued that the state had violated his right to a jury trial as guaranteed by the Sixth Amendment of the United States Constitution. The Supreme Court ruled in favor of Ker, holding that the state of Illinois had violated his right to a jury trial. The Court reasoned that the Sixth Amendment guarantees a defendant the right to a jury trial in all criminal cases, and that the state could not deny this right. The Court also noted that the right to a jury trial is a fundamental right that is essential to a fair trial. The Court's decision in Ker v. Illinois was significant because it established that the right to a jury trial is a fundamental right that must be respected by all states. This decision has been cited in numerous subsequent cases involving the right to a jury trial.

Justice Field delivered the dissenting opinion in Ker v. Illinois, arguing that the state of Illinois had violated the Fourteenth Amendment by denying a fair trial to William Ker. He argued that since Ker was not allowed to present evidence or cross-examine witnesses during his trial, he was denied due process and equal protection under the law as guaranteed by the Constitution. Furthermore, Justice Field asserted that if states were allowed to deny defendants their right to a fair trial without consequence then it would set a dangerous precedent for other states and undermine public confidence in our judicial system. He concluded by stating that while there may be exceptions where such rights can be limited, this case did not meet those criteria and thus should have been overturned on appeal.