Exhibit 99.1 Isabella Bank Corporation Reports Second Quarter 2025 Results MT. PLEASANT, MICHIGAN — July 24, 2025 — Isabella Bank Corporation (Nasdaq: ISBA) ("Isabella" or the "Company") reported second quarter 2025 net income of $5.0 million, or$0.68 per diluted share, compared to $3.5 million, or$0.46 per diluted share, in the same quarter of 2024. Core net income (non-GAAP) in the second quarter of 2025 totaled $4.1 million, or$0.55 per diluted share, compared to $3.5 million, or$0.46 per diluted sha ...