Welch served as the first principal of Michigan State Normal School (now Eastern Michigan University) from 1851 to 1865. In 1859, he married Eunice P. Buckingham and they had three children.
In 1865, Welch moved to Pensacola, Florida, and eventually to Jacksonville, Florida, for unspecified health reasons. There, he established a lumber mill and engaged in orange growing. His wife, Eunice, died in 1867. In 1868, he married Mary Beaumont Dudley, with whom he had two more children.
As part of the post-Civil War Reconstruction, Florida was readmitted to the United States in 1868. Welch was elected by the legislature to the U.S. Senate as a Republican. He served in the Senate for less than nine months but declined renomination.
Instead, he chose to accept an appointment as the first president of Iowa State Agricultural College. He served as college president from 1869 to 1883 before resigning. Welch felt that Iowa State was a progressive institution and was proud that it allowed women to attend classes.[2]
From 1885 until his death, Welch served as a psychology professor at Iowa State. In 1889, he died at his summer home in Pasadena, California. Adonijah Welch is interred at Iowa State College Cemetery in Ames, Iowa.
Welch Hall, named after him, was constructed in 1895 at Michigan State Normal School (now Eastern Michigan University). Welch Hall is the second-oldest building on the EMU campus. The building is designed in the Georgian Revival style.
The building's original name was the "Training School"; it served as the Teacher Training School from 1896 to the 1960s. During the building's lifetime, Welch has served as classroom space and various department offices. Due to poor maintenance, the building was closed during the 1980s and almost demolished. In 1984, Welch Hall was added to the National Register of Historic Places. Today, Welch Hall has been restored. It houses EMU's executive offices, which include the Office of the President.
