I can find no reason from your pictures to dispute your identification. Another identifier you can look for is a funky small if the leaves are crushed.  As for how careful you need to be.?  Pretty careful. Long pants, long sleeves, heavy gloves, and do not forget the eye protection. You have several options for removing it depending on the size of the hemlock. You should be able to save neighboring plants, at least most of them.

Poison hemlock is a biennial which means a two-year life cycle. The first year it stays a reasonably small rosette of ferny leaves. The next year the same leaves will form and then, later in the season a very tall flower stalk will shoot up and it will bloom and set seed. This must be prevented of course. Several websites recommend just mowing it if it is still in the rosette stage. Yours are probably too big for that by now though. Digging is effective if you can get enough of the taproot. Right after a good rain or watering is helpful.  One website suggests enclosing the top of the plant in a heavy-duty plastic trash bag, tying it off near the ground, then digging it out.

Chemical control is possible, 2,4-D with dicamba is recommended or glyphosate is effective. Read and follow all label directions, wear protective clothing, including eye protection, and protect neighboring plants from overspray if you use a spray mechanism. These are non-selective poisons.

Below are several links to websites with lots of information about poison hemlock and how to remove it. Each one only takes a couple minutes to read and they are full of information.

OSU Extension: Poison hemlock emerging around the state, including Fairfield County (yahoo.com)

How to Identify Poison Hemlock and its Lookalikes • New Life On A Homestead

Poison Hemlock (Conium maculatum) : USDA ARS

IPCW Plant Report – California Invasive Plant Council (cal-ipc.org)

Exotic Species: Poison Hemlock (U.S. National Park Service) (nps.gov)

Good Luck!