BARONY of TATESHAL (ancestors of)
EON or YON (Eudo),[f] son of SPIREWIC, SPIRVIC or SPIRUWIN, in 1086 held lands as a tenant-in-chief in cos. Lincoln, Norfolk and Suffolk. [Complete Peerage XII/1:645, (transcribed by Dave Utzinger)]
[f[ The name usually latinised as Eudo had lost the d before the 12th century, hence the alternative forms Heunnus and Heo; see Appendix K, p. 32, in this volume it occurs as Eon, Eoun, Ion, Ioun, Iun, Yon, Yum, Yun.
----------
Note: This citation does not say he was of Tattershall, but the next generation (Hugh) said he succeeded to Tattershall no later than 1118, so Eon/Eudo is thus connected with it.