As more trading ports were established in the interior of Kenya and Uganda it more officers were needed.

According to Robert Foran (1962), the earliest history of East-Central Africa provided the background for the creation of the British East African Company at the end of 1902.

The British East African Protectorate, with the exception of the ten-mile wide coastal strip leased from the Sultan of Zanzibar was proclaimed a crown colony in July 1920 changing its name to Kenya Colony, while the title of the force changed to Kenya Police Force.

It is notable that up to 1907, the Kenya Police was organized along military lines and the training was military in nature. In 1906, the Kenya Police was legally constituted by the Police Ordnance.

In order to improve police performance, the then Governor, Sir Hayes Saddler appointed a committee to look into the affairs of the Kenya Police Force.

One of the committee's recommendations was the establishment of the Police Training School in Nairobi . In 1909, Captain W.F.S. Edwards noted that the military element had been promoted at the expense of police training, as a result of which a training depot was established in Nairobi in 1911 together with a small fingerprint section.

The First World War interrupted this development of the Force in 1914 where the Kenya Police were deployed in military service to fight alongside British soldiers.

After the end of the war in 1918, the Police Force began to be reorganized. This entailed increasing personnel and creating better administrative and residential housing. During the same period, schools were established for African Education, thereby improving literacy in the Force so that by 1940, there were many literate African officers.

In 1926, the Criminal Intelligence Unit was established with the sole responsibility of collecting, tabulating and recording the history and data of criminals, undesirable and suspicious persons.

In the same year, the Railway Police Unit was also established to specifically deal with prevention and detection of offences in the railways from the coast to Kisumu, including Kilindini Harbour and branch lines.

As the years progressed, the scope of police activities increased. It was called upon to deal with traffic problems such as accidents and parking. The police were also called upon to deal with cattle rustling in the countryside.

In 1946, the Police Force was placed under the office of the Attorney General. The police officers' powers were increased, and to cope with the new development, a new Police Training Depot was opened in Maseno.

As a preparation for the Second World War, the recruits were deployed in Northern Frontier Districts to counter the threat from Italian Somali Land and Ethiopia . In addition to fighting alongside regular soldiers, the Kenya Police acted as guides, interpreters and carried out reconnaissance missions in the enemies' territories.

In 1948, several important developments were made in the Force. The Kenya Police Reserve Emergency was formed as an auxiliary of the Force. This Unit used armored cars and was deployed in trouble spots. To improve the effectiveness of crime control, a dog section was also introduced in 1948 and the General Service Unit established and deployed in troubled areas in emergency situations.

In 1949, the Police Airwing was formed to carry out duties of communication and evacuation of sick persons to hospitals and was made part of the permanent Police Force in January 1953.

After the declaration of the state of emergency in 1952, there was an immediate increase in personnel to cope with the situation and in response to the Mau Mau insurgency. In 1953, a commission was formed to review the organization, administration and expansion of the Force.

In 1957, the Police Headquarters building was opened and in 1958 the Force was integrated within the Ministry of Defense. In the period prior to independence, the Kenya Police was greatly involved in the maintenance of law and order during political meetings and at the height of the independence election period.