senators were elected by the state legislatures every two years, with one-third beginning new six-year terms with each congress. preceding the names in the list below are senate class numbers, which indicate the cycle of their election. in this congress, class 1 meant their term began in the last congress, requiring reelection in 1862; class 2 meant their term began with this congress, requiring reelection in 1864; and class 3 meant their term ended with this congress, requiring reelection in 1860.