In 1921, Illinois Governor Lennington “Len” Small started paving Illinois highways which had previously been dirt roads that were nearly impassable much of the year. With the increase in automobiles, motor traffic needed to be regulated to keep these new roads in good shape.

On June 24, 1921, the 52nd General Assembly of the State of Illinois authorized the Department of Public Works and Buildings to hire a "sufficient number of State Highway Patrol Officers to enforce the provisions of the Motor Vehicle Laws." The Illinois State Police (ISP) was officially formed in 1922, known then as the Illinois Highway Maintenance Police, and consisting of eight officers patrolling on surplus World War I Harley-Davidson motorcycles. The Department has since grown and evolved into what it is today – a nationally recognized, premier law enforcement, public safety, and criminal justice agency. Beginning in 1922, each era has built upon the efforts and accomplishments of the previous era, embarking upon a journey of continuous improvement and excellence.

Over the years, the ISP has continually changed in size and organizational structure to provide an increased number of services in the most efficient manner to the people of Illinois. On June 29, 1923, the 53rd General Assembly authorized the creation of the Illinois Highway Maintenance Police with 100 officers. In 1931, the Illinois General Assembly authorized the Bureau of Criminal Identification and Investigation, which would ultimately become the Illinois State Police Forensic Lab System and the Bureau of Identification.