The first police department on The Land was established in LY 238, in Tonad. Each village has a Chief of Police (elected by the village's citizens to a term of five years), while most districts within a village have a deputy chief (appointed by the chief). The next rank is detective (sometimes called "inspector"), below which are patrolmen (sometimes called "constables").
In the years leading to the establishment of the first police department, crimes had been becoming more common, particularly as new types of blades began to be forged specifically for use as weapons. It was becoming more common as well, naturally, for citizens to purchase weapons to use for self-defense. This eventually led to people banding together to hunt down criminals, and capture them to stand trial (though at the time there was no actual court system, which wasn't established until 899). In fact there were few specific laws in any village (at the time the first police department was established, there were only two villages, but the rarity of written laws held true, to a lesser degree, even in the time the courts were established, centuries later), though of course everyone knew that things like theft, assault, or murder were wrong. In those days, accused criminals would be prosecuted and defended by representatives who had no legal training, as there was no such occupation as "lawyer" then, nor "judge." Guilt or innocence, and the nature of punishment if necessary, would be determined by a vote of whatever citizens showed up for the trials.
But in the late 220s and early 230s, it became clearer that private citizens could not be expected to carry out justice on their own; not only was it too time-consuming for people who had other jobs and responsibilities, but there was also too much chance for people to abuse the concept of crimefighting, to commit criminal acts themselves and cover it up by saying their victims had acted against them first. Already in those days there were people who considered themselves adventurers, and it was often these people who had the most free time and experience in fighting, and were therefore best suited to dealing with criminals. (Though of course, many who called themselves adventurers were also what people might call criminals, themselves.) And so, adventurers as well as ordinary citizens (particularly the ones who most often served as defenders or prosecutors) realized it would be necessary to create an official group to deal with crime. Members of this group would be called police (which is both the singular and plural form), and the department would be headed by a Chief of Police. The police would be paid by the public fund (a concept first introduced in 117, see Currency of the Land), as would any expenses necessary to the performance of their jobs, such as building headquarters, providing weapons, etc.
Once the PD was established, they began regular patrols, and would apprehend criminals to be held in cells at their headquarters until they could stand trial. This eventually led to the village voting on more specific laws as well as standardized punishments for breaking those laws, one of the most common punishments being imprisonment. This, naturally, meant it was necessary to build a jail, and to hire guards to work there. (But as mentioned, this increase in laws and trials was still not yet sufficient to prompt the organizing of a court system.) Crime soon began dropping in Tonad, which led First Village to establish its own police department in 242. Since then, every subsequent village to be founded has established its own police department.
Around 362, piracy began springing up around the east coast of First Land, as new port villages were founded. To deal with this, a branch of the police department in Ship was established, called the Coast Guard. Other port villages soon established such a branch in their own police departments, and in 371, they collectively broke off from the police to form their own organization, but retained close ties to the PD.
The court system was not the only new innovation in law enforcement that came in 899. The courts were in large part created in response to the rise of gangs, which also inspired every village's PD (which heretofore had had very little interaction) to form a unifying body called InterVil. (Merfolk, it should be noted, are known to have their own way of dealing with crime, possibly involving police, though they did not send delegates to represent them in InterVil.)