Many of the yokai on this website are featured in my book, The Night Parade of One Hundred Demons. I am currently working on a second book, The Hour of Meeting Evil Spirits, which will be published in 2014. There are many other excellent resources, online and in print, for yokai information. These are the very best of them that I have found.

ONLINE

Sawaki, Sūshi. The Illustrated Volume of a Hundred Demons. 1737. <http://en.wikipedia.org/wiki/Hyakkai_Zukan>

Toriyama, Sekien. The Illustrated Night Parade of a Hundred Demons. 1776. <http://en.wikipedia.org/wiki/Gazu_Hyakki_Yagyō>

Toriyama, Sekien. The Illustrated One Hundred Demons from the Present and the Past. 1779. <http://en.wikipedia.org/wiki/Konjaku_Gazu_Zoku_Hyakki>

Toriyama, Sekien. Supplement to The Hundred Demons from the Present and the Past. 1780. <http://en.wikipedia.org/wiki/Konjaku_Hyakki_Shūi>

Toriyama, Sekien. The Illustrated Bag of One Hundred Random Demons. 1784. <http://en.wikipedia.org/wiki/Gazu_Hyakki_Tsurezure_Bukuro>

atelier CROMAGNON. <http://www.cromagnon.jp>

Hyakumonogatari Kaidankai. <http://hyakumonogatari.com>

Database of Images of Strange Phenomena and Yokai. International Research Center for Japanese Studies. <http://www.nichibun.ac.jp/YoukaiGazouMenu>

Folktale Data of Strange Phenomena and Yokai. International Research Center for Japanese Studies. <http://www.nichibun.ac.jp/YoukaiDB>

BOOKS

Hearn, Lafcadio. In Ghostly Japan. Boston: Little, Brown, and Co., 1899.

Hearn, Lafcadio. Kwaidan: Stories and Studies of Strange Things. Boston: Houghton, Mifflin and Co., 1904.

Shigeru, Mizuki. Mujara. Tokyo: Softgarage Inc., 1998.

Murakami, Kenji. Yōkai Jiten. Tokyo: Mainichi Newspaper Co. Ltd, 2000.

Toriyama, Sekien. Toriyama Sekien Gazu Hyakki Yagyō Zen Gashū. Tokyo: Kadokawa Shoten Publishing Co., 2005.

Yumoto, Koichi. Yokai Museum: The Art of Japanese Supernatural Beings from YUMOTO Koichi Collection. Tokyo: PIE Books, 2013.