To claim the CHET (Connecticut Higher Education Trust) income tax deduction on your Connecticut state taxes, follow these steps:
Open your CT state return and continue until you get to the screen Here's the income that Connecticut handles differently
Scroll down to Education
Select CHET Contributions
CHET is a state-sponsored, tax-advantaged 529 college savings plan that's helping families and individuals plan for the cost of higher education. Connecticut families can take an income tax deduction (up to $5,000 for single filers, $10,000 for joint filers) on contributions to CHET accounts