After he left office in 1864, Kirkwood moved to a new house on Wyoming Road in Iowa City (now Kirkwood Avenue) and practiced law.
About this time Kirkwood sold his share of the mill, part of it to his brother, William, and part to Valentine Miller.
In 1865-1867, he served the remainder of James Harlan’s term in the U.S. Senate, and served in the Senate again from 1877 to 1881.
Between his separate terms as a Senator, he was again the Governor of Iowa from 1876 to 1877.
 He resigned as governor in 1877 to begin his second term as U.S. Senator.
In 1881, Kirkwood resigned his Senate seat to become Secretary of the Interior under President James Garfield.
He served as Interior Secretary until 1882.
He unsuccessfully ran for Congress in 1886.

Kirkwood died in 1894 in Iowa City, and is buried in Oakland Cemetery.
After he left office in 1864, Kirkwood moved to a new house on Wyoming Road in Iowa City (now Kirkwood Avenue) and practiced law. About this time Kirkwood sold his share of the mill, part of it to his brother, William, and part to Valentine Miller. In 1865-1867, he served the remainder of James Harlan’s term in the U.S. Senate, and served in the Senate again from 1877 to 1881. Between his separate terms as a Senator, he was again the Governor of Iowa from 1876 to 1877.  He resigned as governor in 1877 to begin his second term as U.S. Senator. In 1881, Kirkwood resigned his Senate seat to become Secretary of the Interior under President James Garfield. He served as Interior Secretary until 1882. He unsuccessfully ran for Congress in 1886.
Kirkwood died in 1894 in Iowa City, and is buried in Oakland Cemetery.
Samuel J. Kirkwood