I retired in June 2018. Where do I put that information and start noting the retirement checks? I receive 3 checks.

[june1416]

Turbo Tax deluxe

[MichaelL1]

The only area that might ask for retirement date is when the 1099R is entered to compute the taxable amount of the pension. 

However if box 2a is entered on the 1099R and that amount is the taxable amount the retirement date might not be necessary.

The program already knows your age, so there is not much change on taxes when retired.