People are attracted to wealth—especially a rich person’s relatives. “A man never knows how many relatives he has until he becomes successful in life” was cited in Mr. Punch, His Origin and Career (1870). “If a man wants to know how many relatives he has, let him die and leave a million dollars toward paving the debt of the United States,” an American newspaper stated in 1877. “At the risk of perpetrating an Irish bull it may be said that a rich man never knows how many relatives he has until he is dead,” an 1887 newspaper stated. It is not known if anyone in particular coined the adage.
 
“A poor man never knows how many poor relatives he has until he becomes suddenly rich,” the San Diego (CA) Union published as a “Pointed Paragraph” in 1936 and 1939. “Howard Spitzer: ‘It is only after a man gets rich that he discovers how many poor relatives he has’” was cited in The Canadian Jewish Chronicle in 1953.
     
 
Google Books
Mr. Punch, His Origin and Career
By Mark Lemon
London: Printed by Jas. Wade
1870
Pp. 8-9:
A man never knows how many relatives he has until he becomes successful in life; then he has friends for the asking, and persons who have ever rendered him a service take especial delight in reminding him of their existence.
 
29 March 1877, Freeborn County Standard (Albert Lea, MN), pg. 4, col. 2:
If a man wants to know how many relatives he has, let him die and leave a million dollars toward paving the debt of the United States. An old fellow of Hoboken, who supposed he had no relatives in the world, did that the other day, and an inconsolate widow and affectionate piece have already come to the front.
 
24 May 1878, The Anglo-American Times (London), pg. 13, col. 1:
A pleasant entertainment is suggested for a millionaire. If he wants to know how many relatives he has, let him disappear for a short time, giving out that he is dead.
 
5 December 1887, The Daily Gazette (Burlington, IA), pg. 1, col. 8:
At the risk of perpetrating an Irish bull it may be said that a rich man never knows how many relatives he has until he is dead.
 
25 June 1896, Bloomington (IL) Leader, pg. 7, col. 2:
A MAN never knows how many relatives he has scattered over the country until he receives some great good fortune.
 
15 July 1897, Denver (CO) Post, pg. 4, col. 2:
An ex-Canadian convict, who says he is a brother, is the latest claimant for some of the Barnato millions. All of which goes to show, as the Irishman puts it, that a man never knows how many relatives he has till he dies and leaves a fortune.
 
8 June 1916, Bay City (MI) Daily Times, “The Salzburg Sage,” pg. 4, col. 2:
A poor man never knows how many relatives he has until he suddenly becomes rich.
 
Old Fulton NY Post Cards
22 July 1927, The Evening Tribune-Times (Hornell, NY), “Editorial Notes,” pg. 4, col. 2:
It is said that ten thousand Swedes are now trying to claim kinship with Lindbergh. A fellow never knows how many relatives he has until he gets rich or does something to make him famous.
 
2 July 1936, San Diego (CA) Union, pg. 9, col. 5:
A poor man never knows how many poor relatives he has until he becomes suddenly rich.
 
26 March 1939, San Diego (CA) Union, “Pointed Paragraphs,” pg. 6-C, col. 7:
A poor man never knows how many poor relatives he has until he becomes suddenly rich.
 
Google News Archive
16 January 1953, The Canadian Jewish Chronicle (Montreal, Quebec), “Our Film Folk” by Leon Gutterman, pg. 16, col. 1:
Howard Spitzer: “It is only after a man gets rich that he discovers how many poor relatives he has.”
     
Google Books
14,000 Quips and Quotes:
For Speakers, Writers, Editors, Preachers and Teachers
By E. C. McKenzie
Grand Rapids, MI: Baker Books
1990
Pg. 443:
It is only after a man gets rich that he discovers how many poor relatives he has.