The purpose of "The State of Computer Science in Illinois High Schools Series" is to analyze the landscape, structures, and pathways to and through computer science (CS) education in Illinois and to create a baseline by which to measure the expansion of CS education in the coming years. The series will include five reports, each analyzing a different aspect to CS education: (1) the CS education landscape; (2) the CS student body characteristics; (3) the CS teacher workforce; (4) student outcomes as they relate to CS coursework; and (5) variations in CS course offerings by high school districts. Throughout "The State of Computer Science in Illinois High Schools Series" the authors will be assessing equity in Illinois high school CS education using the CAPE framework. The CAPE framework is a lens developed by CS education researchers to assess equity in CS education using four components: capacity for, access to, participation in, and experiences of CS education. At the end of each report in the series, the authors devote a section to what the report's findings suggest about the state of Illinois high school CS through this lens. Data for this series was provided by the Illinois State Board of Education (ISBE). The dataset consists of student-level data of every Illinois high school student who enrolled in at least one CS course between the school years 2017-2018 (SY 2018) and 2021-2022 (SY 2022). This first landscape report explains the evolving patterns and characteristics of CS course enrollment over this period. The analyses completed are descriptive in nature and are meant to provide an overview of recent statewide trends.