The Inje University Genealogy Library is by far the best source of Korean genealogical records available.
http://genealogy.inje.ac.kr/main/main.php

The Inje University Genealogy Library’s online library of JokBo is incredible. They have recently changed their policy and no longer require registration to access the books online! They did this to make JokBo research resources more broadly available to everyone. This is wonderful.

There is still one hurdle for English speakers who want to use this library. Viewing the books requires installing a browser add-on / application that only works with Windows Explorer (no problem) and the Korean version of Windows. Please note that the Korean version of Windows is not referring to an English version of Windows with a Korean font installed.

There are two approaches to overcome the “Korean Windows” hurdle. 1) Install Korean Windows on a computer. I got a little $250 laptop (smaller than a laptop, actually) that has a Korean version of Windows XP CE on it and that worked well. I also emulated a Korean version of Windows 2000 using VirtualBox (free software at https://www.virtualbox.org/wiki/Downloads) on a more powerful PC running an English version of Windows 10 and that worked well, too.