Henry B. Clow was the son of William and Harriet (Cartlidge) Clow. His father was born in England in 1835 and came to the U.S. at age 15, first residing in Portsmouth and then Manchester, where he established one of the first hosiery mills in the state. The family then relocated to Lakeport, where William and his son, Henry founded the Wm. Clow & Son Hosiery Mill in 1883. William died in 1899 . The mill (Bayside Mill in Lakeport) was destroyed by fire in 1905, at which time Henry purchased the Gilford Hosiery Mill on Union Avenue in Laconia and moved the business there. He continued to operate the mill until 1929.

Henry's known siblings were Thomas B., Sarah A., Emma E., Maria D., Frank W., and Alice M. (See William Clow for details)

Henry married Cora B. Lane (3/11/1860 - 10/24/1894) in 1881 and they had the following children: Harry L.. (1882), Alonzo L. (1884), Inez (1886), Bessie L. (1890), and Annie E. (abt. 1894). His first wife, Cora, died in 1894 at age 34 and he married Nellie Eveline Judd (11/28/1878 - 4/27/1929) in 1898. Nellie's children were Cora M. (1899), Louise H. (abt. 1903), Stephen J. (abt 1904), and Everett S. (abt. 1906). Several of the children are buried in the family lot. His son, Harry L., was associated with his father in the hosiery business, as were other members of the family. Inez (Clow) Tyler was proprietor of Clow Sisters gift shop on Union Avenue in Lakeport. Henry resided at 205 Washington Street, Lakeport.

The Clows owned "Little Island" on Paugus Bay from 1895 - 1918, and during that time it became known as Clow Island. For a number of years after its sale, it continued to be referred to as Clow Island, even though its official name was always Little Island.