Robert Crozier (October 13, 1827 - October 2, 1895) was a United States Senator from Kansas. Born in Cadiz, Ohio, he attended the public schools and an academy. He studied law in Carrollton, Ohio and was admitted to the bar in 1848. He was prosecuting attorney of Carroll County from 1848 to 1850 and moved to Leavenworth, Kansas in 1856, where he established the Leavenworth Daily Times and also engaged in the practice of law. He was a member of the Territorial council, 1857-1858 and was appointed United States attorney for the district of Kansas by President Abraham Lincoln, an office he held from 1861 to 1864, when he resigned. He was chief justice of the Kansas Supreme Court from 1864 to 1867, and was subsequently a cashier and manager of the First National Bank of Leavenworth.
Crozier was appointed as a Republican to the U.S. Senate to fill the vacancy caused by the resignation of Alexander Caldwell and served from November 24, 1873, to February 12, 1874, when a successor was elected. He was not a candidate for election, and resumed the practice of his profession in Leavenworth. He was district judge of the first judicial district of Kansas from 1876 to 1892 and was a member of the board of directors of the Kansas Historical Society from 1886 to 1889. He died in Leavenworth in 1895 and was interred in Mount Muncie Cemetery.