REGULATORY CAPITAL (Details) $ in Thousands	Jun. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 1,859,031	$ 1,920,388
Minimum Capital Requirement	667,908	694,987
Minimum To Be Well Capitalized	$ 964,756	$ 1,003,870
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1253	0.1243
Minimum Capital Requirement	0.0450	0.0450
Minimum To Be Well Capitalized	0.0650	0.0650
Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,081,781	$ 2,143,138
Minimum Capital Requirement	890,544	926,650
Minimum To Be Well Capitalized	$ 1,187,391	$ 1,235,533
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1403	0.1388
Minimum Capital Requirement	0.0600	0.0600
Minimum To Be Well Capitalized	0.0800	0.0800
Total Capital to Risk Weighted Assets, Amount
Actual	$ 2,390,209	$ 2,459,847
Minimum Capital Requirement	1,187,391	1,235,533
Minimum To Be Well Capitalized	$ 1,484,239	$ 1,544,416
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1610	0.1593
Minimum Capital Requirement	0.0800	0.0800
Minimum To Be Well Capitalized	0.1000	0.1000
Leverage Ratio of Tier 1 Capital to Average Assets, Amount
Actual	$ 2,081,781	$ 2,143,138
Minimum Capital Requirement	$ 702,084	$ 718,334
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1186	0.1193
Minimum Capital Requirement	0.0400	0.0400
Busey Bank
Common Equity Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,168,464	$ 2,150,048
Minimum Capital Requirement	665,889	692,654
Minimum To Be Well Capitalized	$ 961,839	$ 1,000,500
Common Equity Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1465	0.1397
Minimum Capital Requirement	0.0450	0.0450
Minimum To Be Well Capitalized	0.0650	0.0650
Tier 1 Capital to Risk Weighted Assets, Amount
Actual	$ 2,168,464	$ 2,150,048
Minimum Capital Requirement	887,852	923,539
Minimum To Be Well Capitalized	$ 1,183,802	$ 1,231,385
Tier 1 Capital to Risk Weighted Assets, Ratio
Actual	0.1465	0.1397
Minimum Capital Requirement	0.0600	0.0600
Minimum To Be Well Capitalized	0.0800	0.0800
Total Capital to Risk Weighted Assets, Amount
Actual	$ 2,312,314	$ 2,287,179
Minimum Capital Requirement	1,183,802	1,231,385
Minimum To Be Well Capitalized	$ 1,479,753	$ 1,539,231
Total Capital to Risk Weighted Assets, Ratio
Actual	0.1563	0.1486
Minimum Capital Requirement	0.0800	0.0800
Minimum To Be Well Capitalized	0.1000	0.1000
Leverage Ratio of Tier 1 Capital to Average Assets, Amount
Actual	$ 2,168,464	$ 2,150,048
Minimum Capital Requirement	700,802	716,476
Minimum To Be Well Capitalized	$ 876,002	$ 895,596
Leverage Ratio of Tier 1 Capital to Average Assets, Ratio
Actual	0.1238	0.1200
Minimum Capital Requirement	0.0400	0.0400
Minimum To Be Well Capitalized	0.0500	0.0500

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