Do not compost poison hemlock in your home compost pile. The compost will not be safe to use. 

"a recently created poison hemlock fact sheet states:
Hand-removed plants should not be burned or added to mulch or compost piles intended for use in areas where additional exposure is likely, as it takes several years for the toxins to dissipate, even in dried plants parts. . . . It should be made clear that the intent of this composting precaution is for preventing dermal exposure when handling the compost. No intention was meant for protecting the soil from possible toxicity as it relates to growing produce."  https://hyg.ipm.illinois.edu/article.php?id=1327

You’re welcome!
Thank you for asking!
And be careful out there. 
btw, you can also consult with your local OSU Extension educator in Hamilton County, Joe Boggs.  He’s written several excellent articles - with helpful photos- about poison hemlock/wild parsnip/giant hogweed, that you can look up in BYGL. https://bygl.osu.edu/
Joe Boggs, Adjunct Assistant Professor, Department of Extension<personal data hidden>https://hamilton.osu.edu/people/joe-boggshttps://bygl.osu.edu/<personal data hidden>Office: Ohio State Extension, Hamilton County5093 Colerain Ave., Cincinnati, OH 45223-1072