The Grand Jury can also be traced to the time of the Norman conquest of England in 1066. There is evidence that the courts of that time summoned a body of sworn neighbors to present crimes that had come to their knowledge. Since the members of that accusing jury were selected from small jurisdictions, it was natural that they could present accusations based on their personal knowledge.

Historians agree that the Assize [court session or assembly] of Clarendon in 1166 provided the ground work for our present Grand Jury system. During the reign of Henry II (1154-1189), to regain for the crown the powers usurped by Thomas Becket, Chancellor of England, 12 "good and lawful men" in each village were assembled to reveal the names of those suspected of crimes. It was during this same period that juries were divided into two types, civil and criminal, with the development of each influencing the other.

The oath taken by these jurors provided that they would carry out their duties faithfully, that they would aggrieve no one through enmity nor deference to anyone through love, and that they would conceal those things that they had heard.

By the year 1290, these accusing juries were given the authority to inquire into the maintenance of bridges and highways, defects of jails, and whether the Sheriff had kept in jail anyone who should have been brought before the justices. "Le Grand Inquest" evolved during the reign of Edward III (1368), when the "accusatory jury" was increased in number from 12 to 23, with a majority vote necessary to indict anyone accused of crime.

In America, the Massachusetts Bay Colony impaneled the first Grand Jury in 1635 to consider cases of murder, robbery and wife beating. As early as 1700, the value of the Grand Jury was recognized as opposing the Royalists. These colonial Grand Juries expressed their independence by refusing to indict leaders of the Stamp Act (1765), and refusing to bring libel charges against the editors of the Boston Gazette (1765). A union with other colonies to oppose British taxes was supported by the Philadelphia Grand Jury in 1770.

By the end of the Colonial Period, the Grand Jury had become an indispensable adjunct of Government: "they proposed new laws, protested against abuses in government, and wielded the tremendous authority in their power to determine who should and who should not face trial."

Public support for Grand Juries, sustained through the Revolutionary Period, began to wane in the early 1800's. Adoption of the Fourteenth Amendment in 1868, made it illegal to "deprive any person of life, liberty or property without due process of law." As interpreted by some states, this amendment no longer required prosecution of crimes by Grand Jury indictment nor prohibited direct accusation by a prosecutor. California is still one of the states that allows prosecution to be initiated by either a Criminal Grand Jury indictment or judicial preliminary hearing.

San Mateo does not impanel a Criminal Grand Jury. If the Civil Grand Jury ascertains that there is an indictable offense, then a separate Criminal Grand Jury will be impaneled.

The first California Penal Codes contained statutes providing for a Grand Jury, to be impaneled quarterly, at the same time as the trial jurors were drawn. Early Grand Juries investigated local prisons, conducted audits of county books and pursued matters of community interest. The role of the Grand Jury in California is unique. The statutes passed in 1880 allowed their duties to include investigation of county government by a Grand Jury beyond alleged misconduct of public officials. Only California and Nevada mandate that Grand Juries be impaneled annually to function specifically in a watchdog capacity over county government.