Isaac Welsh was born July 20, 1811, in Belmont County, Ohio. He was raised on a farm, and had little formal education. As an adult, he moved to Beallsville in Monroe County, and was in merchandising, but soon returned to Belmont. He was a Whig until that party collapsed.[1]
In 1857, and 1859, he was elected to the Ohio House of Representatives for the 53rd and 54th General Assembly as a Republican.[2] In 1861, he was elected from the 20th District to the Ohio Senate in the 55th General Assembly.[3]Presidential elector for Grant/Colfax in 1868[4]
Welsh was elected state treasurer in 1871, and again in 1873. He died November 25, 1875, and his son Leroy Welsh was appointed to serve the remaining weeks of his second term.[1]
Welsh was married to Mary A. Armstrong of Belmont County.[5]