Exhibit 99.1 PACKAGING CORPORATION OF AMERICA REPORTS FIRST QUARTER 2024 RESULTS Lake Forest, IL, April 22, 2024 – Packaging Corporation of America (NYSE: PKG) today reported first quarter 2024 net income of $147 million, or$1.63 per share, and net income of $155 million, or$1.72 per share, excluding special items. First quarter net sales were $2.0 billion in 2024 and 2023. Diluted earnings per share attributable to Packaging Corporation of America shareholders Three Months Ended March 31, 2024 2023 Chang ...