Per CT Form CT-1040 Connecticut Resident Income Tax Instruction Booklet, page 27:

Am I Eligible for the Credit for Income Taxes Paid to Qualifying Jurisdictions?

If you are a resident of Connecticut and if any part of your income was taxed by a qualifying jurisdiction, you may be able to claim a credit against your Connecticut income tax liability for qualifying income tax payments you have made.

Qualifying Jurisdiction.

A qualifying jurisdiction includes another state of the United States, a local government within another state, or the District of Columbia. A qualifying jurisdiction does not include the State of Connecticut, the United States, or a foreign country or its provinces (for example, Canada and Canadian provinces).

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