The name "Leas" appears to be English in origin. According to the Historical Research Center:
Leas is an "English surname belonging to that category of surnames that are locative in origin, being derived from the place where the original bearer once lived or held land. In this instance, the surname Lease was applied to "lees", from the Old English "loes" meaning "field". The name may also be derived from any of the various places with the element "leas", the plural from of the Old English "leah" meaning "wood, clearing" such as Lees near Ashton-under-Lyne and Leece near Barrow-in-Furness."I think that this is a bit speculative but plausible. One name research place that I tried once claimed that Leas was a variant of McLeash and another says it comes from the name Gillies and that it is Scottish in origin. I have been to England, Scotland and Ireland and I did not find many people with the name Leas in the phone books in the cities that we visited, so if it is English in origin the family did not thrive there.
There is a park called "Leas Beach Park" near Norfolk, England http://www.theleasbeachpark.co.uk and there is an area called "The Leas" near Folkestone, England (see the postcard below), maybe the name came from these areas.
The history of the Leas family in the United States is detailed in the book titled "Leas Genealogy" published by Fay Leas on October 17, 1950. The book was printed by the Waterloo Press in Waterloo, Indiana. This is the second edition of the book, the first edition was published on July 20, 1930. I don't know if there was ever a newer version.
The first reference to a Leas family in America is in the "Original List of Persons of Quality" which refers to an expedition to Barbados in 1635. I have been to Barbados myself and examined some genealogical records at the museum there. I found records of a George Leas and of one or two generations of Leas'. After two generations the name is no longer mentioned. It is not clear if this Leas family is related to those living in the United States today.
From the Leas Genealogy, John Leas I and Leonard Leas, apparently brothers, came to America from England. Leonard Leas was granted a land patent in 1743, so he arrived in the 1740s. John Leas came to America in 1750.
There are clear records about John Leas II, who was born in 1755 and died 1847. John Leas II was a private in the 4th Battalion of the Infantry of Pennsylvania during the revolutionarily war. He was married to Sophia Ziegler and they had 15 children. The Leas Genealogy follows the lines of three of John II's children. The book also follows the line of a Benjamin Leas who is thought to be the brother of John II. There is also discussion of a Daniel Leas who was born in Germany in 1778 and who came to the United States with his parents when he was young.
It is possible that all of the Leas families in the United States are descendant from either the parents of Leonard and John I or from the parents of Daniel Leas. It is unknown if the two branches were related or if there were other Leas families that came to the United States.
David Leas has a great web page with lots more information about the Leas family at:
The blazon of arms above, comes from the Historical Research Center and is said to be the blazon of arms of the Leas family or a variant (they say that Lease, Lees, and Leese are variants).