He is married to Luise Friederike Charlotte Hedwig von Hoym.
They got married on February 27, 1771 at Wolfenbüttel.
http://trees.ancestry.com/pt/AMTCitationRedir.aspx?tid=114784053&pid=725
Franz Jacob von Cramm<br>Gender: Male<br>Birth: Circa 1751 - Germany<br>Death: Sep 4 1771<br>Parents: Franz Jacob von Cramm, Anna Wilhelmine Magdalene von Cramm (born von Korsigk)<br>Wife: Charlotte Friederike Hedwig von Cramm<br>Siblings: Sophia Magdalena (born von Cramm), Dorothea Luise von Korsigk (born von Cramm), Freda Antoinette (born von Cramm), Charlotte Wilhelmine von Knuth (born von Cramm)
http://trees.ancestry.com/pt/AMTCitationRedir.aspx?tid=159732775&pid=1278/ Ancestry.com