In the early colonies policing took two forms:
The watch system was composed of community volunteers whose primary duty was to warn of impending danger. Boston created a night watch in 1636, New York in 1658 and Philadelphia in 1700. The night watch was not a particularly effective crime control device. Watchmen often slept or drank on duty. While the watch was theoretically voluntary, many “volunteers” were simply attempting to evade military service, were conscript forced into service by their town, or were performing watch duties as a form of punishment. Philadelphia created the first day watch in 1833 and New York instituted a day watch in 1844 as a supplement to its new municipal police force (Gaines, Kappeler, and Vaughn 1999).
Augmenting the watch system was a system of constables, official law enforcement officers, usually paid by the fee system for warrants they served. Constables had a variety of non-law enforcement functions to perform as well, including serving as land surveyors and verifying the accuracy of weights and measures. In many cities constables were given the responsibility of supervising the activities of the night watch.
These informal modalities of policing continued well after the American Revolution. It was not until the 1830s that the idea of a centralized municipal police department first emerged in the United States. In 1838, the city of Boston established the first American police force, followed by New York City in 1845, Albany, NY and Chicago in 1851, New Orleans and Cincinnati in 1853, Philadelphia in 1855, and Newark, NJ and Baltimore in 1857 (Harring 1983, Lundman 1980; Lynch 1984). By the 1880s all major U.S. cities had municipal police forces in place.
These “modern police” organizations shared similar characteristics: (1) they were publicly supported and bureaucratic in form; (2) police officers were full-time employees, not community volunteers or case-by-case fee retainers; (3) departments had permanent and fixed rules and procedures, and employment as a police officers was continuous; (4) police departments were accountable to a central governmental authority (Lundman 1980).
[...]
The key question, of course, is what was it about the United States in the 1830s that necessitated the development of local, centralized, bureaucratic police forces? One answer is that cities were growing. The United States was no longer a collection of small cities and rural hamlets. Urbanization was occurring at an ever-quickening pace and old informal watch and constable system was no longer adequate to control disorder. Anecdotal accounts suggest increasing crime and vice in urban centers. Mob violence, particularly violence directed at immigrants and African Americans by white youths, occurred with some frequency. Public disorder, mostly public drunkenness and sometimes prostitution, was more visible and less easily controlled in growing urban centers than it had been rural villages (Walker 1996).