A trier of fact is an individual, or group of individuals, who ascertain questions of fact in a legal proceeding.
Normally, a trier of fact refers to either a jury, or a judge in trials without a jury. In bench trials, administrative hearings, boards and commissions, a judge is the trier of fact. In jury trials, the jury determines facts of the case and is considered to be the trier of fact.
The individual(s) responsible for determining the facts in a case is (are) considered to be the trier of fact. In a jury trial, the role of the judge is exclusively to make legal decisions while the jury finds the facts in the case and applies them to the relevant laws or statutes as instructed by the judge; in this case, the jury is considered the trier of fact.
Essentially, the trier of fact is the party who is responsible for listening to all of the evidence, testimonies and arguments of a case, and making the decision as to whether or not the defendant is guilty or innocent of the charges or accusations.
When the trier of fact is a jury, jury members are chosen from the available pool of jurors in a county. It is considered a civic duty for all eligible adults in a county to potentially serve as jurors. These adults can be summoned by the court when needed, in accordance with the law.