On the evening of December 12, 1829, he left his Manhattan hotel to mail a letter at a New York City dock and was never seen again. Lansing was 75 years old and was presumed drowned or perhaps murdered. A cenotaph was erected at Albany Rural Cemetery. His widow died in 1834.
His fate was a major mystery in New York State at the time, rivaled only by the disappearance of William Morgan, the anti-Mason writer, in 1826 in upstate New York. In the last century it has somehow become rather forgotten, especially with the disappearance of New York State Justice Joseph Force Crater in 1930. There has been only one major clue to Lansing's disappearance that has appeared since his death. After his death in 1882 the memoirs of Thurlow Weed, former Republican political leader in New York State, were published by Weed's grandson T.W. Barnes. Weed wrote that Lansing had been murdered by several prominent political and social figures who found he was in the way of their projects.
Weed was told this by an unnamed individual, who showed him papers to prove it, but begged Weed not to publish these until all the individuals had died. Weed said they were all dead by 1870, but he found that their families were all highly respected, and upon advice of two friends he decided not to reveal the truth because it would hurt innocent people. And that was the last anyone ever heard of a possible resolution to the mystery. It is unknown if Weed actually received the truth.
Read more about this topic: John Lansing, Jr.