The first courthouse was a small structure, sixteen feet square. It was originally erected by Henry Martin, on a location that would eventually become Decatur Baptist College. When the small town of "Taylorsville" (Decatur's original name) began being platted by Colonel Absolom Bishop, the father of Decatur, he patterned it after the City of McKinney in Collin County. The small building was moved to the northeast corner of the square and was the first house on the hill.
The second courthouse, built on the square, was a large two-story building. On the night of November 26, 1881, the building burned; it was thought to be arson.
The present courthouse was completed in 1896 at a cost of $110,000 (an amount thought by many to be extravagant. The officials approving the construction were not re-elected).
Colonel Absolom Bishop raised a flag on the hill where the courthouse now stands, boasting that his choice for the courthouse had won the recent election. Disillusioned with then President Taylor, he changed the city's name to Decatur, after naval hero Stephen Decatur.
Bonds were issued on May 16, 1895. The stone was precut and each piece numbered and then shipped from Burnet County, Texas. The stones were raised by a windlass pulled by donkeys walking in a circle. The building is constructed of pink granite with interior of Vermont marble; it has been pronounced "architecturally perfect."
All indebtedness was paid off in 1945, and the building was modernized in the 1960's. The outdoor mercury vapor lamps were installed in 1968.
In 1975, the second County Jail was erected on the site where the original courthouse stood. It is now the County Clerk's Office.