According to an article in 'Kokon yoranko' (an illustrated encyclopedia) publihed in 1905-1907, there had already been a description of Inoko mochi as an item for one of annual events in the Imperial court in the book of 'Kuroudo-shiki' (rules of officials in charge of classified documents) compliled by TACHIBANA no Hiromi.
「古今要覧稿」（明治38年～40年刊行）に亥の子餅の項目があり、「蔵人式」（橘広相撰）の中に、禁中年中行事の1つとして記されている。