Substitute Senate Bill No. 458, also known as Public Act No. 26-19, amends existing law to designate various days and months for public observance in the state. Notably, the bill replaces "Indian" with "Indigenous Peoples'" in the proclamation of the last Friday in September as Indigenous Peoples' Day, which honors Native Americans and their contributions to American life. Additionally, it changes the observance of Lobster Roll Day from the third Saturday to the third Sunday of September.

The bill further introduces several new observances, including Hartford Whalers Day on January 11, Topical Steroid Withdrawal Awareness Day on February 3, and 6888th Central Postal Directory Battalion Day on March 4, among others. Other new designations include Henry Breault Day on March 8, Eid al-Fitr on the first day of Shawwal, Progressive Supranuclear Palsy Awareness Month in May, Hiram Bingham IV Day on July 17, Ovarian Cancer Awareness Month in September, Good Neighbor Day on September 28, and Military Suicide Remembrance and Awareness Day on September 30. Each of these observances allows for suitable exercises to be held as designated by the Governor.