 On 16 May 1814 Fergusson was again promoted without purchase, becoming lieutenant-colonel of the 3rd (Buffs) Regiment's 2nd battalion.Following the Buffs' reduction in 1816, Fergusson studied at the Royal Military College, before taking an appointment as lieutenant-colonel of the 88th Regiment of Foot.In 1825, Fergusson exchanged into the 52nd (Oxfordshire) Regiment of Foot, commanding it in England, Ireland, Nova Scotia, Gibraltar, and the West Indies, until 1839, receiving his promotion to full colonel in 1830.