The designed landscape has remained similar in layout since the improvements undertaken in c.1814 from map evidence. Paintings at the house by John Wilson show the house before the Gillespie addition and those by Severn in 1873 show the old stable-block just to the south-west of the house.
It is known that a tower house was standing on the site of the present house by the 14th century. The estate at that time was divided and the tower house which forms the nucleus of the present Kilkerran was then known as Barclanachan and was the home of a branch of the Kennedys. Kilkerran tower house lay two miles away and Fergus Fergusson obtained a charter confirming him in the lands at Kilkerran from Robert the Bruce who reigned between 1306-29. It remained the home of the Fergussons until 1650, when their estates were sequestered by Cromwell. Though the estate was later restored to the Fergussons, the family were deeply in debt through their support of the Royalist cause. In 1700 Sir Alexander Fergusson yielded Kilkerran and the family titles to his cousin John Fergusson who had acquired Barclanachan in 1684 through his marriage with Jean Whytefoord, whose father had purchased it from the Kennedys. He joined the two estates and transferred the name Kilkerran to Barclanachan rebuilding the house and incorporating the old tower. In 1703 he was created a baronet of Nova Scotia by Queen Anne.
As early as 1711, John's son, James, who was later to become a keen agricultural improver, started tree planting on his father's estate and by 1715 he had commenced a programme of hill planting. In 1726 he married Jean Maitland, the granddaughter of the 5th Earl of Lauderdale, and succeeded to Kilkerran in 1729 when he carried out further improvements to the house and grounds. The mansion was virtually rebuilt as a large, symmetrical elongated H-plan house with giant pilasters on the north front, to the designs of James Smith. William Adam is recorded as supplying fireplaces in 1744. Plans for the policies were drawn up in 1721, by William Boutchart, 'an exact plan of Kilkerran', and in 1744 'a plan of enclosures' by William Edgar. Both of these plans show elaborate formal designs but reference to General Roy's map of 1750 would suggest that if either had been implemented it had been changed by 1750. Roy's map shows the house with the main road to the north, but further south than it is today, and with drives in avenues diagonally to the house from the north-west and the north-east. There is a compound to the south of the house, where the offices were later situated, and a block of hill planting further south. The only remaining feature which today corresponds to either of those plans is the Great Diagonal lime avenue to the SSE of the house which is absent on the Roy plan but appears on the 1st edition OS map. James became an advocate, later a Lord of Session under the title Lord Kilkerran (1749). He died in 1759 and was succeeded by his son Adam.
Adam, the 3rd Baronet, was MP for Ayrshire from 1774-96; he made claim to the Earldom of Glencairn but was defeated in the Lords. He was succeeded by his nephew, James, who commenced large schemes of alterations to the house and grounds, and who was a founder of the Ayrshire Agricultural Association. James Gillespie Graham carried out extensive alterations to the house; a new entrance was made in the west front and the round-ended wings were added. The Toddy Burn immediately to the west of the house was covered over and many park trees were planted. In 1814 John Hay submitted a design for a walled garden. The 4th Baronet died in 1838 and was succeeded by his son Charles. His grandson James, the 6th Baronet, succeeded in 1849 and commissioned David Bryce to carry out further alterations to the house, including the billiard room along the north front. Sir James was an MP from 1854-68, then spent long periods abroad as Governor of South Australia from 1868-73 and of New Zealand from 1873-74, and of Bombay from 1880-85. Writing from New Zealand he asked his factor to arrange for a new garden to be made south of the house comprising 'a few flowerbeds laid out on the hill'. The sunken garden was made at this time, and the west front lawn levelled with the spoil. This grandiose and expensive interpretation was to cost the gardener his job on Sir James' return. Further improvements were made to Kilkerran in 1873-6 designed by Brown and Wardrop, when principally the south front was altered so as to enlarge the dining room and new stables were built further away from the house, and many of the specimen conifer trees and parkland trees were planted at this time. Between 1880- 1913 the house was let, during which time however, the garden was maintained. General Charles Fergusson succeeded in 1907 and he also became Governor General of New Zealand between 1924-30. He was succeeded by his son Sir James in 1951. The house was redecorated in 1956 with Schomberg Scott as the architect. Sir James was keeper of the Records of Scotland from 1949-69 and put the estate plans and records into good order. He was also author of 'Lowland Lairds' published in 1949. The present laird is his son, Sir Charles Fergusson, 9th Baronet.