Drysdale was accepted as a sept of Douglas by CDSNA at its organization in 1975 based on the original list from the book Scots Kith and Kin.
Documentation for this name being a sept of Douglas is based on the following account found in Family Record of the Name of Dingwall Fordyce in Aberdeenshire (1885). It should be noted, however, that the following story does not account for the genesis of the name Drysdale but only for the connection of Drysdale to the House of Douglas.
23. Drysdales (Vale of Devon).
The River Dryfe, on which the Town of Lockerby in Dumfriesshire is situated, helps to water the Parish of Drysdale, and this is probably the region from which Drysdales scattered over other parts have originally come. For a number of years they have been well known in Fife and in Kinross and Clackmannan, although the name is not given by Sir Robert Sibbald among the heritors of the two former counties in his time. The enterprising manufacturers of the name in Tillycoultry, etc., trace their descent, however, to a family of Douglases from the Parish of Drysdale, who kept the assumed name after the necessity for concealment passed away. The story, which they believe to be genuine, is given in a document preserved and handed down, copied first by Symon Drysdale of the Haugh of Dollar in 162o; then by Robert Drysdale of Tillycoultry in 17o8, and since then renewed at different times. It runs thus:
"On the twentieth day of May, one thousand five hundred and three years, we, Thomas, William and James Douglas, sons of the departed Thomas Douglas of Brushwood Haugh in the Parish of Drysdale and Shire of Dumfries, left our native place for the reason here assigned, viz.: defending our just and lawful rights against our unjust neighbour Johnstone of Greenstone Hill,'who being determined to bring water to his mill through our property, and having obtained leave of his friend the King [James IV], began his operations on the sixteenth of May. We prevented him by force. The next day he brought twenty of his vassals to carry on the work. We with two friends and three servants (eight in all) attacked Johnstone with his twenty; and in the contest fourteen of his men were killed along with their base leader. A report of these proceedings was carried to the King and we were obliged to fly (the tocsin being sounded). We took shelter under the shadow of the Ochil Hills in a lonely valley, on the River Devon. After having lived there two full years we returned home in disguise, but found all our property in the possession of Johnstone's friends, and a great reward offered for our lives. We, having purchased a small spot called the Haugh of Dollar and changed our names to the name of our native parish, are clearly in mind to spend the residue of our days under the ope of the Ochils, and wish the name of Drysdale to flourish in the lonely valley. The King passed through this with his court on the 12th of June, fifteen hundred and six, going from Stirling to Falkland, and dined at Halliday's Green (an eastern neighbour), but we were not known."
Alexander Drysdale, the first of the family mentioned on these pages of whom we have heard, was born in 1692 and died in 1755, but whether he belonged to the neighbourhood of Hawkslaw, near Coldstream, where he and his wife, Isobel Halyburton, originally resided, has not been ascertained.
A similar story can be found in the Douglas Archives. The two versions vary little in substance.
The Douglas Archives, Drysdale. http://www.douglashistory.co.uk/history/Septs/drysdale.htm
Fordyoe, Alexander D. Family Record of the Name of Dingwall Fordyce in Aberdeenshire: Showing Descent from the First Known Progenitor of Either Name -- Both Direct and Collateral. with Appendix Containing Notices of Individuals and Families Incidentally Referred to. Fergus, Ontario, Canada: n.p, 1885. Print. Digital copy found: http://books.google.com/books?id=Jx8IAAAAQAAJ&pg=PR35&lpg=PR35&dq=Thomas+Douglas+,+of+Brushwood+Haugh&source=bl&ots=sV1Z0PeCLs&sig=e4zwptaVCtLLyRZnHGP4EsnOCYw&hl=en&sa=X&ei=fqJqUt3vLqHL2gW3pYGYAw&ved=0CGMQ6AEwCQ#v=onepage&q=Thomas%20Douglas%20%2C%20of%20Brushwood%20Haugh&f=false