Hello Jonah,
Please refer to the following forum link where a similar issue has been answered :
http://our.componentone.com/groups/topic/how-to-get-footer-summar-row-in-c1flexgrid/
For creating groups in C1FlexGrid, you can make use of the C1FlexGridGroupPanel Class.
Please refer to the following documentation links for more information regarding the same :
Also, you can refer to our "GroupPanel" product sample available at :
http://our.componentone.com/samples/wpf-grouppanel/
Hope this helps.
Regards,
Reema