I usually go to the Surnames database for info on family name origins. Here is Carey
There are, unusually, four distinct origins for this name, found as "Cary", "Carey" and "Carye". The first of these is of Welsh and Cornish origin, as a variant of the locational name "Carew", from any of the minor places named from the Welsh "caer" fort, and "rhiw", hill. The Carey family who have held the estate of Antony in Cornwall throughout the Middle Ages derive their name from this source. The second possible origin is English and also locational, from any of the places in Devon and Somerset so called from being situated on the River Cary, thought to be so named from the Celtic root-word "Car", meaning "love", "liking" - so, perhaps, "pleasant stream". The third source is French, and another locational name, from the manor of "Carrey", near Lisieux, Normandy. The marriage of "Henry Crey" and "Ann Morgan" is recorded in London in 1545. Finally, Carey is an Anglicized form of the old Gaelic O' Ciardha, the Gaelic prefix "O" indicating "male descendant of", plus the personal byname Ciardha from "ciar" dark or black. The Careys were lords of Carbury (Co. Kildare), up to the mid 12th Century. The first recorded spelling of the family name is shown to be that of Hamo de Kan, which was dated 1205 "Pleas before the King or his Justices", Somerset, during the reign of King John, known as "Lackland", 1199 - 1216.

Read more: http://www.surnamedb.com/Surname/carey#ixzz3r6ZISwXY

The other source I like is the distribution maps of the 1881 and 1998 census at the National Trust.

Here is the link to the National Trust distribution map of 1881 census.
http://gbnames.publicprofiler.org/Ma...y=GB&type=name

Interestingly if you look at the 1998 census the name is much more numerous in Scotland in more modern times.
http://gbnames.publicprofiler.org/Ma...y=GB&type=name