The following is a summary of acts which authorized boundary changes for Decatur County.
- Acts of 1845-46, Chapter 62, Section 3, appointed John H. Houston and William H. Storm, of Decatur County, and William F. Doherty and the present county surveyor of Benton County, as Commissioners to run the line between the two counties, and clearly mark the same, commencing at the Tennessee River on the northeast corner of Decatur County and run westerly, making reports to their respective county courts which shall allow each of them such compensation as to them seems reasonable and proper. This amendment is conditioned upon Decatur County being created.
- Acts of 1849-50, Chapter 92, declared that the line between Decatur and Henderson Counties should conform to the line commencing at the point designated in the act passed January 19, 1848, and run in a southwesterly direction (so as not to approach Lexington nearer than 12 miles) to the line known as the Brown line; thence south with that line to the Hardin County line; and the citizens east of that line are entitled to all the rights and privileges and are subject to all the liabilities as are other citizens of Decatur County.
- Acts of 1855-56, Chapter 173, Section 4, established the line between Decatur and Hardin Counties as beginning at a point where the Counties of Henderson, Hardin, and Decatur join; running thence with Hardin County line to Doe Creek; thence down the said creek to the Tennessee River; thence down the said river to the south boundary of Decatur County, and all that part of Hardin County contained within the lines designated, and situated north and west of the Tennessee River, and below Doe Creek is attached to Decatur County, all citizens living in that area being declared residents of Decatur County. Section 8 of this act transferred all the lands of E. Lee out of Henderson County and into Decatur County.
- Acts of 1868-69, Chapter 36, changed the boundary lines between Decatur and Wayne Counties so as to include all that portion of Wayne County lying west of the Tennessee River in the County of Decatur.
- Acts of 1871, Chapter 33, detached all that area known as "Eagles Nest Island" from Hardin County and attached the same to Decatur County. This same act then moved all the lands belonging to William White which were in Decatur County over to Hardin County so as to place all his lands wholly within Hardin County.
- Acts of 1873, Chapter 100, rearranged the county lines between Decatur and Henderson Counties so that all the lands and residences belonging to J. Henry Thomas and J. H. Dodd were included wholly within Decatur County.
- Acts of 1877, Chapter 14, established subject, however, to the approval of two-thirds of the voters in the area affected, a new county by the name of Hanes which would be composed of parts of Benton, Carroll, Henderson, and Decatur Counties, as the parts were described therein. A commissioner would be named, and the county, if formed, would be part of the 12th Judicial Circuit.
- Acts of 1877, Chapter 58, moved the home and farm belonging to Allen Steyers out of Benton County and into Decatur County.
- Acts of 1881, Chapter 130, changed the line between Decatur and Henderson Counties beginning at the county line at the land or lands, known and formerly owned by G. M. Morgan, and now owned by Noah Williams, running east with the line of John F. Chumley, continuing with the same until it strikes the present county line at and with T. Lemon's line.
- Acts of 1883, Chapter 221, changed the line between Decatur and Benton County so that the Benton County line would run from its northeast corner south up the Tennessee River about one mile to a slough; thence west with the Bark Road, on a dividing ridge, to H. C. Walker's; thence north with the west boundary line of H. C. Walker's farm across with the west boundary line of Alfred Tippitt's farm to the Benton County line near Richard Odle's.
- Acts of 1885, Chapter 13, altered the lines between Decatur and Henderson Counties. Beginning where the county line crosses the north boundary line of J. C. P. Myracle's home tract of land, known as the Cox land; running thence west continuously with said lines to its northwest corner; thence south to its southwest corner; thence east to where the county line crosses the south boundary of the above mentioned land, so as to include all of the J. C. P. Myracle tract in Decatur County.
- Acts of 1891, Chapter 51, moved the residence and farm belonging to D. A. Gossett out of Decatur County and into Benton County.
- Private Acts of 1939, Chapter 600, changed the boundary lines between Decatur and Benton Counties so that four acres and 52 poles belonging to J. B. Odle shall all be included in Benton County.