Several gun collector publications list Isaac King as a Somerset County, Pennsylvania gunsmith due to his whitesmith advertisement in the January 8, 1818 issue of the "Somerset Whig" newspaper. The advertisement mentions that Isaac King has guns for sale.
Vaughn E. Whisker provided the following transcript of the 1818 advertisement in an article titled "Co. Had 30 Gunmakers-Gunsmiths" in the November 1971 issue of the Somerset County "Laurel Messenger". A transcript (with slightly different punctuation and capitalization) is also provided in Kauffman's 1960 book "The Pennsylvania-Kentucky Rifle".
A negative image of the original newspaper advertisement is provided on page 120 of James B. Whisker's 1990 book "Arms Makers of Pennsylvania".
A reference to the Isaac King advertisement is included in the March 3, 1897 issue of the "Somerset Herald" newspaper. Excerpts follow; notice the reference to the gunsmith Adam Lepley.
Here is the definition of a Whitesmith from Webster's 1874 "A Dictionary of the English Language":
I did not find Isaac King in the Somerset Borough or Somerset Township portions of the 1810 or 1820 census records of Somerset County.
The following image is from the 1830 Tanner "Map of Somerset County" which is based on the manuscript 1818 Melish-Whiteside map that was originally prepared by John Wells. I include it here to show the configuration of the town of Somerset in 1818, including the location of the diamond that is referenced in the 1818 Isaac King advertisement. The 1830 map includes the names of east-west streets; those names were missing on the 1818 map. The square was located at the intersection of what are now known as Center and Main streets (40.00753625, -79.07860434).
L. Dietle