Finland
Surname Neoff is based in Finland on surname Neovius and has been used since ca year 1800 until late 1900es, the last holders living in USA. There are also other families in East Europe (Bulgaria, Poland, Hungary) and their descendants around the globe that are not related.
The oldest known male-line ancestor of the family is Thomas Thomason in Renko near Tavasthus. His son Kristian or Kristoffer or Krister born 1717 was the ancestor of all the Neoff family in Finland. The older son Thomas was the ancestor of the Neovius and Nevanlinna families. Both Thomas and Kristian used surname Neovius, latinized from Nyby or New Village or Uusikylä.
See http://www.helsinki.fi/ylioppilasmatrikkeli/henkilo.php?id=6850 for information about Thomas and Kristian.
Adolf Neoff, son of Kristian, shortened his surname first from Neovius to Neov and later through Neof to Neoff as he settled at the Koliseva Frälse in Sysmä. Part of the family changed their surname to Rinne already in 1907 and the rest to either surname Mäyrä based on the farms they owned or surname Neva in 1919. The last persons to change his surname to Neva were Kalle Aleksi Neoff and his mother Wilhelmina in year 1934.
The last holder of surname Neoff based on this Finnish family was Mabel M. Neoff, wife of John Theodore Neoff, who died in 1991, in USA.
Esimerkkinä siitä, millaisia ovat onnistuneet nimien suomalaistuttamiset, mainitsemme tässä niistä muutamia Itä- Hämeestä: ..., Neva — Neoff j.n.e. / Kansalliskirjaston digitaaliset aineistot: Itä-Häme, 23.04.1930, nro 20, s. 1: https://digi.kansalliskirjasto.fi/sanomalehti/binding/1183581/artic... / Viitattu 4.1.2021