PRESENTATION OF FINANCIAL INFORMATION (Policies)	9 Months Ended
Sep. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Consolidation	Basis of Consolidation Tri-State is a taxable wholesale electric power generation and transmission cooperative operating on a not-for-profit basis serving large portions of Colorado, Nebraska, New Mexico and Wyoming. Tri-State was incorporated under the laws of the State of Colorado in 1952. Tri-State has thirty-nine electric distribution member systems ("Utility Members") who are Class A - utility full requirements members to which it provides power pursuant to long-term wholesale electric service contracts. Tri-State has three non-utility members (“Non-Utility Members”). Tri-State's Class A Utility Members and Non-Utility Members are collectively referred to as its “Members.” Tri-State provides wholesale power to its Utility Members at rates determined by its Board of Directors ("Board"), subject to FERC approval or acceptance. Rates are designed to recover all costs and provide margins to increase Utility Members' equity and to meet certain financial covenants, including a debt service ratio ("DSR") requirement and equity to capitalization ratio ("ECR") requirement. The accompanying financial statements reflect the consolidated accounts of Tri-State, its wholly-owned and majority-owned subsidiaries, and certain variable interest entities for which Tri-State or its subsidiaries are the primary beneficiaries. See Note 17 – Variable Interest Entities. Tri-State's consolidated financial statements also include its undivided interests in jointly owned facilities. All significant intercompany balances and transactions have been eliminated in consolidation.
Basis of Accounting	Tri-State complies with the Uniform System of Accounts as prescribed by FERC. In conformity with GAAP, the accounting policies and practices applied by Tri-State in the determination of rates are also employed for financial reporting purposes.
Accounting Pronouncement - Not Yet Adopted	Accounting Pronouncement - Not Yet Adopted In November 2024, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2024-03, Income Statement (Subtopic 220-40): Reporting Comprehensive Income - Expense Disaggregation Disclosures. This standard requires public business entities to disclose, in the notes to the financial statements, additional information about specified categories of expenses included in relevant expense captions presented on the face of the income statement. Required disclosures include amounts related to purchases of inventory, employee compensation, depreciation, intangible asset amortization and depletion for both annual and interim periods. In January 2025, the FASB issued ASU 2025-01 which clarified the effective dates of ASU 2024-03. The amendments are effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Tri-State is currently evaluating the impact of ASU 2024-03 on its consolidated financial statement disclosures. Because the amendments affect disclosure requirements only, Tri-State does not expect adoption to have an impact on its consolidated results of operations, financial position or cash flows. Tri-State expects to adopt the ASU 2024-03 disclosure requirements with its Annual Report on Form 10-K for the year ending December 31, 2027. In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832). ASU 2025-10 establishes authoritative guidance for the accounting and disclosure of government grants received by business entities. Under this amendment, a government grant is recognized when it is probable that the entity will comply with the conditions of the grant and that the grant will be received. Grants related to assets are recognized either as deferred income or as a reduction of the carrying amount of the related asset, while grants related to income are recognized in earnings either as other income or as a reduction of the related expense. ASU 2025-10 also establishes disclosure requirements intended to provide users of financial statements with information about the nature, terms and financial statement effects of government grants. ASU 2025-10 is effective for public business entities for annual periods beginning after December 15, 2028. Early adoption is permitted. Tri- State is evaluating the impact that adoption of ASU 2025-10 will have on its consolidated financial statements and related disclosures. In May 2026, the FASB issued ASU 2026-02, Environmental Credits and Environmental Credit Obligations (Topic 818). ASU 2026-02 establishes a comprehensive accounting framework for the recognition, measurement, presentation and disclosure of environmental credits, such as renewable energy credits, and environmental credit obligations. The guidance requires environmental credits that meet specified criteria to be recognized as assets, while obligations that may be settled using environmental credits are recognized as liabilities. ASU 2026-02 also requires expanded qualitative and quantitative disclosures regarding the nature, use, valuation and settlement of environmental credits and related obligations. ASU 2026-02 is effective for public business entities for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years. Tri-State is evaluating the effect of adopting ASU 2026-02 on its consolidated financial statements.

PRESENTATION OF FINANCIAL INFORMATION (Policies)

9 Months Ended

Sep. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Tri-State is a taxable wholesale electric power generation and transmission cooperative operating on a not-for-profit basis serving large portions of Colorado, Nebraska, New Mexico and Wyoming. Tri-State was incorporated under the laws of the State of Colorado in 1952. Tri-State has thirty-nine electric distribution member systems ("Utility Members") who are Class A - utility full requirements members to which it provides power pursuant to long-term wholesale electric service contracts. Tri-State has three non-utility members (“Non-Utility Members”). Tri-State's Class A Utility Members and Non-Utility Members are collectively referred to as its “Members.”

Tri-State provides wholesale power to its Utility Members at rates determined by its Board of Directors ("Board"), subject to FERC approval or acceptance. Rates are designed to recover all costs and provide margins to increase Utility Members' equity and to meet certain financial covenants, including a debt service ratio ("DSR") requirement and equity to capitalization ratio ("ECR") requirement.

The accompanying financial statements reflect the consolidated accounts of Tri-State, its wholly-owned and majority-owned subsidiaries, and certain variable interest entities for which Tri-State or its subsidiaries are the primary beneficiaries. See Note 17 – Variable Interest Entities. Tri-State's consolidated financial statements also include its undivided interests in jointly owned facilities. All significant intercompany balances and transactions have been eliminated in consolidation.

Basis of Accounting

Tri-State complies with the Uniform System of Accounts as prescribed by FERC. In conformity with GAAP, the accounting policies and practices applied by Tri-State in the determination of rates are also employed for financial reporting purposes.

Accounting Pronouncement - Not Yet Adopted

In November 2024, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2024-03, Income Statement (Subtopic 220-40): Reporting Comprehensive Income - Expense Disaggregation Disclosures. This standard requires public business entities to disclose, in the notes to the financial statements, additional information about specified categories of expenses included in relevant expense captions presented on the face of the income statement. Required disclosures include amounts related to purchases of inventory, employee compensation, depreciation, intangible asset amortization and depletion for both annual and interim periods. In January 2025, the FASB issued ASU 2025-01 which clarified the effective dates of ASU 2024-03. The amendments are effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Tri-State is currently evaluating the impact of ASU 2024-03 on its consolidated financial statement disclosures. Because the amendments affect disclosure requirements only, Tri-State does not expect adoption to have an impact on its consolidated results of operations, financial position or cash flows. Tri-State expects to adopt the ASU 2024-03 disclosure requirements with its Annual Report on Form 10-K for the year ending December 31, 2027.

In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832). ASU 2025-10 establishes authoritative guidance for the accounting and disclosure of government grants received by business entities. Under this amendment, a government grant is recognized when it is probable that the entity will comply with the conditions of the grant and that the grant will be received. Grants related to assets are recognized either as deferred income or as a reduction of the

carrying amount of the related asset, while grants related to income are recognized in earnings either as other income or as a reduction of the related expense. ASU 2025-10 also establishes disclosure requirements intended to provide users of financial statements with information about the nature, terms and financial statement effects of government grants. ASU 2025-10 is

effective for public business entities for annual periods beginning after December 15, 2028. Early adoption is permitted. Tri-

State is evaluating the impact that adoption of ASU 2025-10 will have on its consolidated financial statements and related disclosures.

In May 2026, the FASB issued ASU 2026-02, Environmental Credits and Environmental Credit Obligations (Topic 818). ASU 2026-02 establishes a comprehensive accounting framework for the recognition, measurement, presentation and disclosure of environmental credits, such as renewable energy credits, and environmental credit obligations. The guidance requires environmental credits that meet specified criteria to be recognized as assets, while obligations that may be settled using environmental credits are recognized as liabilities. ASU 2026-02 also requires expanded qualitative and quantitative disclosures regarding the nature, use, valuation and settlement of environmental credits and related obligations. ASU 2026-02 is effective for public business entities for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years. Tri-State is evaluating the effect of adopting ASU 2026-02 on its consolidated financial statements.