If you took a standard deduction last year or itemized sales tax instead of state income tax, your state income tax refund isn’t taxable.
Go to this section in Credit Karma Tax: Income - Form 1099-G
Your state tax refund from last year is taxable if you itemized your state income taxes. Because you received a refund, your state taxes ended up being less than you had claimed as a deduction on your federal return. As a result, all or part of your state refund can become taxable income in the next year.