105 ILCS 5/10-19
Each school board shall annually prepare a calendar for the school term, specifying the opening and closing dates and providing a minimum term of at least 185 days to insure 176 days of actual pupil attendance, computable under Section 10-19.05, except that for the 1980-1981 school year only 175 days of actual pupil attendance shall be required because of the closing of schools pursuant to Section 24-2 on January 29, 1981 upon the appointment by the President of that day as a day of thanksgiving for the freedom of the Americans who had been held hostage in Iran. Any days allowed by law for teachers' institutes but not used as such or used as parental institutes as provided in Section 10-22.18d shall increase the minimum term by the school days not so used. Except as provided in Section 10-19.1, the board may not extend the school term beyond such closing date unless that extension of term is necessary to provide the minimum number of computable days. In case of such necessary extension school employees shall be paid for such additional time on the basis of their regular contracts. A school board may specify a closing date earlier than that set on the annual calendar when the schools of the district have provided the minimum number of computable days under this Section. Nothing in this Section prevents the board from employing superintendents of schools, principals and other nonteaching personnel for a period of 12 months, or in the case of superintendents for a period in accordance with Section 10-23.8, or prevents the board from employing other personnel before or after the regular school term with payment of salary proportionate to that received for comparable work during the school term. Remote learning days, blended remote learning days, and up to 5 remote and blended remote learning planning days established under Section 10-30 or 34-18.66 shall be deemed pupil attendance days for calculation of the length of a school term under this Section.
A school board may make such changes in its calendar for the school term as may be required by any changes in the legal school holidays prescribed in Section 24-2. A school board may make changes in its calendar for the school term as may be necessary to reflect the utilization of teachers' institute days as parental institute days as provided in Section 10-22.18d.
The calendar for the school term and any changes must be submitted to and approved by the regional superintendent of schools before the calendar or changes may take effect.
With the prior approval of the State Board of Education and subject to review by the State Board of Education every 3 years, any school board may, by resolution of its board and in agreement with affected exclusive collective bargaining agents, establish experimental educational programs, including but not limited to programs for e-learning days as authorized under Section 10-20.56 of this Code, self-directed learning, or outside of formal class periods, which programs when so approved shall be considered to comply with the requirements of this Section as respects numbers of days of actual pupil attendance and with the other requirements of this Act as respects courses of instruction.
105 ILCS 5/10-19