“Eternal vigilance is the condition, not only of liberty, but of everything which as civilized men we hold dear.”

The trial of Charles B. Reynolds for blasphemy (1887)
Context: Liberty is the condition of progress. Without Liberty, there remains only barbarism. Without Liberty, there can be no civilization.
If another man has not the right to think, you have not even the right to think that he thinks wrong. If every man has not the right to think, the people of New Jersey had no right to make a statute, or to adopt a constitution — no jury has the right to render a verdict, and no court to pass its sentence.
In other words, without liberty of thought, no human being has the right to form a judgment. It is impossible that there should be such a thing as real religion without liberty. Without liberty there can be no such thing as conscience, no such word as justice. All human actions — all good, all bad — have for a foundation the idea of human liberty, and without Liberty there can be no vice, and there can be no virtue.
Without Liberty there can be no worship, no blasphemy — no love, no hatred, no justice, no progress.
Take the word Liberty from human speech and all the other words become poor, withered, meaningless sounds — but with that word realized — with that word understood, the world becomes a paradise.

Speech in Boston, Massachusetts (28 January 1852), Speeches Before the Massachusetts Anti-Slavery Society (1853), p. 13. The memorable and oft-quoted phrase, "eternal vigilance is the price of liberty," was not in quotation marks in the printed edition of this speech. The Home Book of Quotations, ed. Burton Stevenson, 9th ed., p. 1106 (1964), notes that "It has been said that Mr. Phillips was quoting Thomas Jefferson, but in a letter dated 14 April, 1879, Mr. Phillips wrote: '"Eternal vigilance is the price of liberty" has been attributed to Jefferson, but no one has yet found it in his works or elsewhere.' It has also been attributed to Patrick Henry."
1850s
Context: Eternal vigilance is the price of liberty — power is ever stealing from the many to the few…. The hand entrusted with power becomes … the necessary enemy of the people. Only by continual oversight can the democrat in office be prevented from hardening into a despot: only by unintermitted Agitation can a people be kept sufficiently awake to principle not to let liberty be smothered in material prosperity.

The History of Freedom in Christianity (1877)

Farewell Address, (4 March 1837), recalling what, by then, had reached the status of a proverb.
1830s

Source: The Genteel Tradition in American Philosophy (1911), p. 58

Often attributed to Jefferson, no original source for this has been found in his writings, and the earliest established source for similar remarks are those of John Philpot Curran in a speech upon the Right of Election (1790), published in Speeches on the late very interesting State trials (1808):
: "It is the common fate of the indolent to see their rights become a prey to the active. The condition upon which God hath given liberty to man is eternal vigilance; which condition if he break, servitude is at once the consequence of his crime and the punishment of his guilt."

*In a biography of Major General James Jackson published in 1809, author Thomas Charlton wrote that one of the obligations of biographers of famous people is

:"fastening upon the minds of the American people the belief, that 'the price of liberty is eternal vigilance' " (in Thomas Usher Pulaski Charlton, The life of Major General James Jackson https://books.google.com.br/books?id=cEcSAAAAYAAJ&pg=PA85&redir_esc=y#v=onepage&q&f=false; F.Randolph, & Co., 1809, p. 85).
Misattributed
Variant: "Eternal vigilance is the price of liberty; power is ever stealing from the many to the few" (from a speech by Wendell Phillips at the Massachusetts Anti-Slavery Society on January 28, 1852; quoted by John Morley, ed., The Fortnightly https://books.google.com.br/books?id=VfjRAAAAMAAJ&pg=PA67&lpg=PA67&dq=%E2%80%9CEternal+vigilance+is+the+price+of+liberty.%E2%80%9D+phillips+speech+anti-slavery&source=bl&ots=H2f8ckIw9o&sig=EukDrduBdK-oQSeY_Gf-VFQ6M54&hl=en&ei=SaxmTN-0H4P98AbioIi0BA&sa=X&oi=book_result&ct=result&redir_esc=y#v=onepage&q=%E2%80%9CEternal%20vigilance%20is%20the%20price%20of%20liberty.%E2%80%9D%20phillips%20speech%20anti-slavery&f=false, Volume VIII, Chapman and Hall, 1870, p. 67).

This has been attributed to Marshall, and he might have used the phrase, but earlier uses exist:
There is an imperialism that deserves all honor and respect — an imperialism of service in the discharge of great duties. But with too many it is the sense of domination and aggrandisement, the glorification of power. The price of peace is eternal vigilance.
Leonard H. Courtney as quoted in The Life Of Lord Courtney (I920) by G. P. Gooch
Courtney's statement however is probably derived from an earlier statement with several variants:
The price of freedom is eternal vigilance.
The price of liberty is eternal vigilance.
Eternal vigilance is the price of liberty.
These have often been attributed to Thomas Jefferson, but also Thomas Paine, Abraham Lincoln, and many others; Alfred Denning in The Road to Justice (1988) states that the phrase originated in a statement of Irish orator John Philpot Curran in 1790: "It is the common fate of the indolent to see their rights become a prey to the active. The condition upon which God hath given liberty to man is eternal vigilance."
Misattributed

[Chaturvedi, Pradeep, Women and Food Security: Role of Panchayats, http://books.google.com/books?id=IuKV5ak57asC&pg=PA46, 1 January 2002, Concept Publishing Company, 978-81-7022-873-8, 46–]

Source: The Great Seesaw: A New View of the Western World, 1750-2000 (1988)