Was John Stuart Mill really influenced by the romantics?

Question

In this passage from Individualism and economic order (1948) (Chapter 1, pp. 25-26), Hayek, although he does not use the term, seems to accuse/disdain Mill for defending an individualism very much influenced by romanticism (aka "German intellectual tradition"):

The point I am trying to make is well illustrated by the apparent paradox that the Germans, though commonly regarded as very docile, are also often described as being particularly individualistic. With some truth this so-called German individualism is frequently represented as one of the causes why the Germans have never succeeded in developing free political institutions. In the rationalistic sense of the term, in their insistence on the development of "original" personalities which in every respect are the product of the conscious choice of the individual, the German intellectual tradition indeed favors a kind of "individualism" little known elsewhere. I remember well how surprised and even shocked I was myself when as a young student, on my first contact with English and American contemporaries, I discovered how much they were disposed to conform in all externals to common usage rather than, as seemed natural to me, to be proud to be different and original in most respects. If you doubt the significance of such an individual experience, you will find it fully confirmed in most German discussions of, for example, the English public school system, such as you will find in Dibelius' well-known book on England. Again and again you will find the same surprise about this tendency toward voluntary conformity and see it contrasted with the ambition of the young German to develop an "original personality," which in every respect expresses what he has come to regard as right and true. This cult of the distinct and different individuality has, of course, deep roots in the German intellectual tradition and, through the influence of some of its greatest exponents, especially Goethe and Wilhelm von Humboldt, has made itself felt far beyond Germany and is clearly seen in J. S. Mill's Liberty.

This article in Quillette directly calls Mill's individualism "romantic individualism".

Though in his romantic individualism Mill despises this trend towards the machine, his rationalist utilitarianism unwittingly makes him its chief cheerleader.

Was John Stuart Mill really influenced by the romantics?

Answer 1

Biographical sources confirm that young Mill was influenced by romantic thinkers, like Coleridge. See J.S. Mill: Life:

"Mill suffered, aged twenty, a “mental crisis”.Though such episodes were to recur throughout his life, his initial recovery was found in the poetry of the Romantics. A new side developed to Mill’s character, and he now emphasised the importance of the culture of the feelings as well as the need for social reform. Mill particularly valued Wordsworth during this period—though his new interests quickly led him to the work of Coleridge, Carlyle, and Goethe. Mill’s acquaintance with these thinkers gave him a lasting openness to Romantic thought—and an acute awareness that the Enlightenment philosophy with which he had been brought up only contained “one side of the truth” (Autobiography, I: 169). His primary philosophic goal became, and would throughout his life remain, to integrate and reconcile these opposing schools of philosophy."

What is the influence of "German romantic/idealist" thinkers on Mill's philosophy, and especially economics thought?

"Mill’s entire philosophical outlook is informed by a spirit of naturalism. Mill’s naturalism involves the claim that human beings and their minds are wholly a part of nature. As such, they are subject to causal laws in just the same manner as the rest of natural world—empirical study of the mind, Mill holds, reveals that it is governed by the laws of associationistic psychology. Mill’s associationism differs in key respects from that of his predecessors. Such modifications of his associationistic inheritance were, in part, a reaction to points made by the Germano-Coleridgean school. His account, nevertheless, remains firmly within the tradition of British empiricism—and he never wavers from a commitment to the claim that our mental life is governed by causal laws operating in a deterministic fashion."

And see Mill's Political Philosophy: "Mill’s liberalism is committed to democratic political institutions in which the franchise is widespread, private property rights, market economies, equal social and economic opportunity, and a variety of personal and civic liberties. [...] Millian liberalism is not laissez-faire liberalism, and it justifies liberal essentials as a way of promoting the common good."

Hayek dedicated a full book to J.S.Mill: Hayek on Mill: The Mill-Taylor friendship and related writings (Collected Works 16). In it, I have found no reference to Romanticism and a single one to idealism (page 320), that is quite similar the the quote in the OP's post:

John Stuart Mill occupied a unique position for so long because he was not merely the heir and developer of a set of ideas which were in the ascendancy, but was also capable of absorbing and learning from most of the other worthwhile ideas of his age. He started as the product and most faithful disciple of his father who was the most active and forceful expositor of Benthamite utilitarianism. He had behind him years of literary activity as an orthodox utilitarian when, at the age twenty-two, he broke away from all orthodoxy and, after a hard struggle and a severe mental crisis, established himself as an independent thinker. Though utilitarianism would continue to provide the general mental framework of his thought, Mill incorporated into it suggestions derived from Saint-Simonian socialism and Comtean positivism over the following years. These elements were derived from Burke and German idealism [emphasis mine] through Coleridge and Carlyle, much of the French liberal thought of the period leading up to the 1848 revolution and— most important for the understanding of the development of his political philosophy— Alexis de Tocqueville.

Thus, in conclusion, Mill's "individualism" is influenced by German idealism, but it seems that Hayek uses "Romanticism" in a loosely way.