He was the son of Alexander Cottin (died 1794) of Hertfordshire; his sister Mary Ann married George Thackeray.

Her parents were Thomas James Storer (1747–1792) (as John James in Kelly), and his wife Elizabeth Proby, daughter of John Proby, 1st Baron Carysfort, and maid-of-honour to Charlotte of Mecklenburg-Strelitz, the Queen.

The miniature painter William Wood made a pair of paintings of the couple, in 1800.

(The reference only identifies her by the courtesy title, and tentatively suggests a later marriage to Francis Willis, which would have been in 1804.

)[19] There are inconsistencies in versions of the affair, particularly in the record for apartments in the Palace, taking Josiah Cottin to be the "Colonel Cotton" of the 10th Light Dragoons of the Confessions; and with the timeline authors give for the seduction of Julia Storer by Cottin.

[20][16] Some of Wilson's affair with the Member of Parliament Richard Meyler, to 1816, took place at Storer's home.

According to the account in Kelly, "Colonel Cotton" was the father, and Anthony challenged him to a duel.