“Don’t vote—it only encourages them” is a joke that television comedian Jack Paar told in May 1966. During the presidential election year of 1976, the saying was put on buttons and bumper stickers.
 
It is not known who came up with the joke first. A form of the joke with “It only encourages them” was printed in a newspaper comic strip in September 1956. Versions from the 1950s and 1960s have an old lady delivering the comic line.
 
     
18 September 1956, Panama City (FL) News, “Mister Breger” comic strip, pg. 7:
“Don’t look up—it only ENCOURAGES them…”
(A woman advises this to a man, who is looking up at a plane skywriting “VOTE FOR KLUN—”—ed.)
 
Google Books
Transactions and proceedings of the National Association of State Universities
v. 54-61 - 1956
Pg. 74:
(“Whom did you vote for?”
 
“Oh, I never vote. It only encourages them.”)
 
This old lady, Mrs. Grant,...
   
14 August 1965, Cumberland (MD) News, pg. 5, col. 3:
OVERHEARD.
At an exclusive club in Boston: “I didn’t vote at all in the last election. It only ENCOURAGES them!”
 
20 May 1966, Lowell (MA) Sun, “Take a Big Bow, Jack Paar!” by Rick DuBrow, pg. 29, col. 2:
Paar’s hour, “A Funny Thing Happened on the Way to the White House,” literally felt like that current rarity—a live, New York-style television revue. Naturally, of course, the revue was in the Paar vein, with amusing clips blended into the entertainment.
 
His opening monologue was strong. “To those of you who don’t recognize me,” he noted, “my name is Hubert Humphrey.” Concerning his lack of partisanship, he recalled what a little old lady from Maine said: “I never vote. It only encourages them.” 
   
Time magazine
Television: A Funny Thing
Friday, May. 27, 1966
(...)
In his rambling opener, Paar twitted the Vice President: (“it’s like being a travel agent for a Zeppelin”), knocked L.B.J. (“I get the impression that when the President speaks he is speaking under our heads”), and then excused himself from partisan politics: “I am like the little old lady who said: ‘I never vote; it only encourages them.’”
 
Google Books
You may know them as sea urchins, ma’am: writings
By Ray Guy and Eric Norman
Portugal Cove, Nfld.: Breakwater Books
1975, 1976 printing
Pg. 102:
Don’t vote — it only encourages them.
 
Alas, I dare say there’ll be too few following this valuable advice.
   
5 September 1976, New York (NY) Times, “Nonvoters Found Near a Majority; 10 Million Rise Since ‘72 Hinted” by Christopher Lydon, pg. 26:
Originally it was the joke: “Don’t vote—it only encourages ‘em.” But an unusually large group of Americans will act on that principle seriously and consciously by avoiding the polling booths this fall, a new study indicates.
 
Google News Archive
28 October 1976, Ellensburg (WA) Daily Record, pg. 6, col. 8:
This voter
wants “none
of the above”
WALNUT CREEK, Calif. (UPI)—Since Jack Roscoe can’t vote for “none of the above,” he is planning to keep away from the voting booth next Tuesday. In fact, he is handing out buttons saying “Don’t Vote. It Only Encourages Them.”
 
Roscoe, president of the Shortstop Markets, distributes the buttons at the checkout stands of his stores.
 
Roscoe, 48, said he would vote if “we could put down ‘none of the above.’”
 
He said he does not like politicians at any level.
   
Time magazine
Those Who Stayed Away
Monday, Nov. 15, 1976
(...)
In San Francisco, John Roscoe, 46, a grocery chain store president, laughed sardonically: “I’m a three-time loser. In 1964 I voted for the peace candidate —Johnson—and got war. In ‘68 I voted for the law-and-order candidate—Nixon—and got crime. In ‘72 I voted for Nixon again, and we got Watergate. I’m not going to vote this time.”

In interviews with nonvoters across the nation, TIME correspondents noted that while some felt apologetic about abstaining, many were confident that they had taken the only proper action. Los Angeles Attorney Linda Abrams, 26, has been pasting stickers on her private letters that read: DON’T VOTE—IT ONLY ENCOURAGES THEM. A Phi Beta Kappa from U.C.L.A., Linda said, “The only way I would vote now would be if there were four categories: Democrat, Republican, No Preference and Abolish This Office.”
 
Google News Archive
22 March 1977, Milwaukee (WI) Journal, “Graffiti is on an upsurge,” Green Sheet, pg. 2, col. 4:
New York seems to excel in wry comments, many directed against local and central government.
 
“Don’t vote, it only encourages them.”
 
OCLC WorldCat record
Don’t vote : it only encourages them!
Author: David Barber; Bob Brockie
Publisher: North Shore City, N.Z. : Cape Catley, 2004.
Edition/Format: Book : English