This interesting name is of medieval Scottish origin and is locational from the manor or barony of Carstairs in the former county of Lanarkshire. Carstairs was formerly recorded as 'Casteltarres' (1170) which derives from the Middle English 'casteli' a castle and the personal name 'Tarra' or 'Tarres', of uncertain origin. During the Middle Ages, when it became more common to migrate from their villages, often to seek work, people would adopt the placename as a means of identification, thus resulting in a wide dispersal of the name. The following examples illustrate the name development, Petrus de Castellstaris (1351), Thomas Castaris (1536). Carstairs is recorded in America in the late 18th Century, when one Thomas Carstairs, born in Largo, Fife in 1759, a builder and architect, emigrated from Scotland to Pennsylvania in 1784. The first recorded spelling of the family name is shown to be that of Adam de Castrotharis, which was dated 1259, Pardevinan in Lanarkshire, during the reign of King Alexander 111, 1249-1286. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.