You can find maps of these in 1861 for comparison here.
Symons is the main spelling form of all those surnames that derive from the original Symon. This was a popular biblical name in the middle ages. The Symons group of spellings in Cornwall accounted for 62% of Symons/Simmons/Semmens in the 1950s, a proportion unchanged from the mid-1600s, when Symon and Symons comprised 66% of the total. In the early 1500s however, only a handful were not spelt Symon.
Remember, if you want information on a surname that hasn’t appeared in my book or been a subject of a previous blog do let me know.