In the 1859 Iowa State Senate elections, Iowa voters elected state senators to serve in the eighth Iowa General Assembly. Following the expansion of the Iowa Senate from 36 to 43 seats in 1859, elections were held for 27 of the state senate's 43 seats. State senators serve four-year terms in the Iowa State Senate. The general election took place in 1859. Following the previous election in 1857, Republicans had control of the Iowa Senate with 22 seats to Democrats' 14 seats. To claim control of the chamber from Republicans, the Democrats needed to net eight Senate seats.