Etymology and distribution of 公下.

The Japanese surnames etymology dictionary.
https://play.google.com/store/apps/details?id=info.jigensha.jcedfreeGoogle Play で手に入れよう https://apps.apple.com/us/app/id1471109324
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Ratio of 公下.

カンマ区切りで複数の名字を指定できます。

Etymology of 公下

Distribution of 公下
Ranking
1 Ishikawa-ken(0.00239%)
2 Nara-ken(0.000297%)
3 Iwate-ken(0.000286%)
4 Mie-ken(0.000219%)
5 Miyagi-ken(0.000208%)
6 Kyouto-fu(0.000166%)
7 Oosaka-fu(0.000115%)
8 Hyougo-ken(Very rare)
9 Kanagawa-ken(Very rare)