Etymology and distribution of 背口.

Seguchi 【背口】^{レベル2
About 10}  The Japanese surnames etymology dictionary.

Fukuoka-ken . Occupation . A variant of the 筑後谷 . In Fukuoka-ken tells that the pronunciation from Ehime-ken comes from chikugoya to chikudodani around 1920. 筑後谷 Chikugoya reference.