John Casper was 26 when he married Barbara who was 40. Wikipedia gives a wedding date of 6 May 1806. Maryland Compiled Marriages, as well as a couple of other sources, give a date of 17 May 1806. John Casper and Barbara did not have any children.
John Casper's wife became well known part of American folklore by an 1863 poem written by John Greenleaf Whittier. John Casper himself was a well known glove maker, having clients from several surrounding states. His shop was attached to his house in Frederick.
Casper died intestate; his estate was distributed in a Frederick County equity court case after his wife Barbara's death. The case names full siblings Maria B. Ritchie and Rebecca Ebert, and half-siblings (by his mother's second marriage to a Hauser/Houser) Catherine Thomas, Susan Buckey, Louisa Leavy, and Frederick Hauser.
Find A Grave, database and images (https://www.findagrave.com : accessed 28 November 2018), memorial page for John Casper Fritchie (1762–10 Nov 1849), Find A Grave Memorial no. 21385739, citing Mount Olivet Cemetery, Frederick, Frederick County, Maryland, USA ; Maintained by Find A Grave (contributor 8).