The State Police Merit System was established under the Illinois Highway Police Act on July 20, 1949.

With the Senate's consent, Governor Adlai Stevenson appointed a three-member Merit Board (MB) to govern the merit system. No more than two members of the Board could belong to the same political party. Terms of the members were set at six years, with original appointments at two, four, and six years to allow staggered terms and continuity of the board policy.

The Merit Board had three main functions:

1. Establish standards, recruit, select, and certify for appointment qualified applicants whom the Superintendent of the Illinois State Highway Police would appoint to the police force.
2. Establish standards and methods for promotion and certify to the Superintendent of the Illinois State Highway Police candidates eligible for promotion.
3. Act as a hearing board for all charges alleged by the Superintendent of the Illinois State Highway Police against officers when seeking their suspension for more than 30 days, demotion, or discharge.

In accordance with the provision of the Illinois Highway Police Act, the MB established qualifications for state police applicants. The original qualifications stated that an applicant needed to be at least 21 years of age and not more than 35 years of age at the time of appointment. An applicant was required to be a United States citizen with no criminal record, and a resident of Illinois for the two previous years. The minimum height requirement for an applicant was five feet nine inches (5'9") and the maximum height requirement was six feet four inches (6'4"). The U.S. Army standards dictated minimum weight for height, and an applicant weighing more than 35 pounds over Army standard was not eligible. An applicant was required to have a high school diploma or a General Education Development Certificate.

Finally, an applicant was required to be of sound mind and body and of good moral character.