I have also been researching relatives with the last name Korsakov. This surname came to Lithuania from the
Czech Republic. It became Korsakas. Later on a branch moved on to Russia and became Korsakov/Korsakoff. From this family came the Rimski-Korsakovs, Dondukov-Korsakovs and others. The Korsakas/Korsakovs were aristocracy and wealthy. It is pretty easy to find their history on the Web.
By the way, I know Lansford quite well although I don't live there.