Isac, Weyl Schwerzen is mentioned 17 times between 1657 and 1681. His designation in the Stühlingen family tree is 'U1'.

Isac was the earliest member of the Endermettingen branch of the Weyl family. He first received protection in Schwerzen [R4323; 08.16.1657] and from 1674 on to 1681 in Endermettingen [R4378; 03.25.1674]. He is identified as a member of the Weyl family by [R4294; 04.18.1673] and [R3575; 12.31.1680]. But there is no apparent connection to the main branch. His major source of income was cattle dealing. Although not listed explicitly, from a chronological point of view it is possible that Isac came with the `foreign Jews` who arrived at Carnival time 1656 [R2065; 10.17.1656]. .