Conkling was elected to the Illinois House for another two-year term in 1866. He authored the bill that would authorize the construction of a new Illinois State Capitol building. Soon after the Assassination of Abraham Lincoln, Conkling was named one of the first fourteen members of the Lincoln Monument Association, where he served for over thirty years. He was elected a trustee of the University of Illinois for the years 1879 to 1880. In 1890, President Benjamin Harrison named Conkling the Postmaster of Springfield. He served the office for four years.