Senators were elected over a wide range of time throughout 1866 and 1867, and a seat may have been filled months late or remained vacant due to legislative deadlock.

The Republican Party gained two seats, as several of the Southern States were readmitted during Reconstruction, enlarging their majority.

Republican Ira Harris had been elected in February 1861 to this seat, and his term would expire on March 3, 1867.

Notes: Conkling was re-elected in 1873 and 1879, and remained in office until May 17, 1881, when he resigned in protest against the distribution of federal patronage in New York by President James A. Garfield without being consulted.

The crisis between the Stalwart and the Half-Breed factions of the Republican party arose when the leader of the New Yorker Half-Breeds William H. Robertson was appointed Collector of the Port of New York, a position Conkling wanted to give to one of his Stalwart friends.

[9] Incumbent Republican Edgar Cowan, who was elected in 1861, was a candidate for re-election to another term, but was defeated by former Democratic Senator and former United States Secretary of War Simon Cameron, who had previously switched to the Republican Party.