Exhibit 99.1 News Release For further information, please contact: 5790 Widewaters Parkway, DeWitt, N.Y. 13214 Marya Burgio Wlos, EVP & Chief Financial Officer Office: (315) 299-2946 Community Financial System, Inc. Reports First Quarter 2025 Results SYRACUSE, N.Y. — April 29, 2025 — Community Financial System, Inc. (the "Company") (NYSE: CBU) reported first quarter 2025 results that are included in the attached supplement. This earnings release, including supporting financial tables, is also available with ...