After his relief from further service in the field, General Smith remained at New York, awaiting orders, till November 24th, 1864, at which time he was assigned to special duty under the orders of the Secretary of War.  This detail was voluntarily tendered and took him to New Orleans, where he was engaged in looking into the military administration of the department, under Butler and his successors, and in reference to which he made several confidential reports which have never been given to the public.  Perceiving that his military career was practically at an end, and that he was not likely to receive satisfactory recognition on the reorganization of the army, he resigned his volunteer commission on the 4th of November, 1865, and took a leave of absence as a Major of Engineers, from December 15th, 1865, to March 7th, 1867, on which later date his resignation from the army was accepted.  He had meanwhile taken employment as President of the International Ocean Telegraph Company, and had visited Florida, Cuba and Spain for the purpose of obtaining an exclusive concession for a term of years, for laying, maintaining and operating an ocean telegraph cable from Jacksonville to Havana.  He was most successful in his negotiations, and in the construction and management of his lines, till 1873, when he and his associates sold out under advantageous terms to the Western Union Telegraph Company.  For the next two years he resided abroad, mostly in England, with his family.  During this time he visited nearly all the countries of western Europe, where he met and made the acquaintance of many leading men in the highest walks of life.

In May, 1873, General Smith was appointed one of the police commissioners for New York City, which place he filled till December 31st of that year, when he was appointed president of the board.  He held this office till March 11th, 1881, during which time he took an important part in elevating and perfecting the police service.  He was, however, too honest and independent to get on harmoniously with the politicians, and after an open breach with a number of them, including the Mayor, he resigned his position and retired to private life.

While engaged in this service he took an active interest in the presidential campaign.  It will be remembered that the closeness of the vote between Mr. Tilden and General Hayes, and the high degree of tension between the opposing parties and their managers, filled the country with alarm, in the midst of which General Smith was consulted by the friends of Mr. Tilden, with the view of devising measures against the possibility of a subversion of the government by military or arbitrary power, but fortunately the device and action of the Electoral Commission averted all danger of that sort.  The timid and vacillating behavior of Mr. Tilden during the emergency and afterwards was, however, a powerful factor in the estrangement of his supporters, and did much to bring about the nomination of General Hancock