Thirza is derived from a Hebrew word meaning "pleasantness". Tirzah was one of the five daughters of Zelophehad who are held up as examples of equality for women. The Victorians preferred the form Thirza. Victoria had ascended the throne in 1819, so perhaps strong women's names were in vogue in 1821.
In 1859 Thirza and Jonas emigrated to the USA and settled in Illinois where their youngest son Joseph was born.