ZMskyuza

Attributed to "an American President" in Ármin Vámbéry (1884), All the Year Round. It more likely originates in a spoof testimonial that Artemus Ward (Charles Farrar Browne) wrote in an advertisement in 1863:
Posthumous attributions

Source: Speech at a Republican Banquet, Chicago, Illinois, December 10, 1856 http://quod.lib.umich.edu/l/lincoln/lincoln2/1:413?rgn=div1;view=fulltext; see Roy P. Basler, ed., The Collected Works of Abraham Lincoln, vol. 2 (New Brunswick, N.J.: Rutgers University Press, 1953), p. 532

Source: 1860s, Speech at Hartford (1860)
Context: So with John Brown and Harper's Ferry. They charge it upon the Republican party and ignominiously fail in all attempts to substantiate the charge. Yet they go on with their bushwhacking, the pack in full cry after John Brown.

Source: 1860s, Second State of the Union address (1862)

This is probably the most famous of apparently apocryphal remarks attributed to Lincoln. Despite it being cited variously as from an 1856 speech, or a September 1858 speech in Clinton, Illinois, there are no known contemporary records or accounts substantiating that he ever made the statement. The earliest known appearance is October 29, 1886 in the Milwaukee Daily Journal http://anotherhistoryblog.blogspot.com/2009/02/fooling-people-earlier.html. It later appeared in the New York Times on August 26 http://query.nytimes.com/gst/abstract.html?res=F30817FF3E5413738DDDAF0A94D0405B8784F0D3 and August 27 http://query.nytimes.com/gst/abstract.html?res=F00E15FF3E5413738DDDAE0A94D0405B8784F0D3, 1887. The saying was repeated several times in newspaper editorials later in 1887. In 1888 and, especially, 1889, the saying became commonplace, used in speeches, advertisements, and on portraits of Lincoln. In 1905 and later, there were attempts to find contemporaries of Lincoln who could recall Lincoln saying this. Historians have not, generally, found these accounts convincing. For more information see two articles in For the People: A Newsletter of the Abraham Lincoln Association, "'You Can Fool All of the People' Lincoln Never Said That", by Thomas F. Schwartz ( V. 5, #4, Winter 2003, p. 1 http://abrahamlincolnassociation.org/Newsletters/5-4.pdf) and "A New Look at 'You Can Fool All of the People'" by David B. Parker ( V. 7, #3, Autumn 2005, p. 1 http://abrahamlincolnassociation.org/Newsletters/7-3.pdf); also the talk page. The statement has also sometimes been attributed to P. T. Barnum, although no references to this have been found from the nineteenth century.
Variants:
You can fool all the people some of the time, and some of the people all of the time, but you cannot fool all of the people all of the time.
You can fool all of the people some of the time, and some of the people all of the time, but you can't fool all of the people all of the time.
You can fool all the people some time, you can fool some of the people all of the time, but you can not fool all the people all the time.
Disputed

Likely spurious quote, UNVERIFIED ATTRIBUTE - Quoted in The Lexington Observer & Reporter (16 June 1864)
1860s
Variant: I am a slow walker, but I never walk back.

Quoted in 3:439 Herndon's Lincoln (1890), p. 439 http://books.google.com/books?id=rywOAAAAIAAJ&pg=PA439&dq=%22when+i+do+good+i+feel+good%22: Inasmuch as he was so often a candidate for public office Mr. Lincoln said as little about his religious code as possible, especially if he failed to coincide with the orthodox world. In illustration of his religious code I once heard him say that it was like that of an old man named Glenn, in Indiana, whom he heard speak at a church meeting, and who said: "When I do good I feel good, when I do bad I feel bad, and that's my religion."
Posthumous attributions

First attributed to Lincoln in 2002, this seems a paraphrase of a statement in the Lyceum address of 1838, while incorporating language used by Thomas E. Dewey (c. 1944), who said "By the same token labor unions can never be destroyed from the outside. They can only fail if they fail to lend their united support to full production in a free society".
Misattributed

This quote is often misattributed to Lincoln. The earliest instance that Quote Investigator could locate was "in an advertisement in 1947 for a book about aging by Edward J. Stieglitz, M.D". The advertisement for “The Second Forty Years” which ran in the Chicago Tribune newspaper read like this: The important thing to you is not how many years in your life, but how much life in your years! (Compare 1947 March 16, Chicago Tribune, “How Long Do You Plan to Live?”, [Advertisement for the book "The Second Forty Years" by Edward J. Stieglitz, M.D.], p. C7, Chicago, Illinois. (ProQuest)). Source of misattribution: It’s Not the Years in Your Life That Count. It’s the Life in Your Years - Abraham Lincoln? Adlai Stevenson? Edward J. Stieglitz? Anonymous? by Quote Investigator on July 14, 2012 http://quoteinvestigator.com/2012/07/14/life-years-count/
To my way of thinking it is not the years in your life but the life in your years that count in the long run.
Adlai Stevenson II, Address at Princeton University, "The Educated Citizen" (22 March 1954) http://infoshare1.princeton.edu/libraries/firestone/rbsc/mudd/online_ex/stevenson/adlai1954.html. This has also been paraphrased "What matters most is not the years in your life, but the life in your years" and misattributed to Abraham Lincoln and Mae West.
Adlai Stevenson II, "If I Were Twenty-One" in Coronet (December 1955).
Misattributed
Variant: It is not the years in your life but the life in your years that counts.

Quoted in a Edith A. Sawyer (1899), Mary Cameron
Misattributed

1860s, Allow the humblest man an equal chance (1860)
Context: Slavery is wrong. If Slavery is right, all words, acts, laws, and Constitutions against it, are themselves wrong, and should be silenced, and swept away. If it is right, we cannot justly object to its nationality — its universality; if it is wrong they cannot justly insist upon its extension — its enlargement. All they ask, we could readily grant, if we thought Slavery right; all we ask, they could as readily grant, if they thought it wrong. Their thinking it right, and our thinking it wrong, is the precise fact upon which depends the whole controversy. Thinking it right as they do, they are not to blame for desiring its full recognition, as being right; but, thinking it wrong, as we do, can we yield to them? Can we cast our votes with their view, and against our own? In view of our moral, social, and political responsibilities, can we do this?
Wrong as we think Slavery is, we can yet afford to let it alone where it is, because that much is due to the necessity arising from its actual presence in the nation; but can we, while our votes will prevent it, allow it to spread into the National Territories, and to overrun us here in these Free States?
If our sense of duty forbids this, then let us stand by our duty, fearlessly and effectively. Let us be diverted by none of those sophistical contrivances wherewith we are so industriously plied and belabored — contrivances such as groping for middle ground between the right and the wrong, vain as the search for a man who should be neither a living man nor a dead man — such as a policy of "don't care" on a question about which all true men do care — such as Union appeals beseeching true Union men to yield to Disunionists, reversing the divine rule, and calling, not the sinners, but the righteous to repentance — such as invocations of Washington, imploring men to unsay what Washington did.

1960s, Portrait of a Genius As a Young Chess Master (1961)