1860–61 United States Senate elections
The 1860–61 United States Senate elections were held from January 14, 1860, to April 2, 1861. Regularly scheduled elections were held for 23 out of the 68 seats in the United States Senate, and special elections were held in California, Oregon, Maine, Pennsylvania, and Ohio.
Source: Wikipedia — 1860–61 United States Senate elections (CC BY-SA 4.0)