From my investigations so far, there are three principal streams of families in the US that now feature the Terman surname. One is the family that arose from Jewish immigrants from the Ukraine area in the late 19th Century. Members of that heritage have been frequent in the Cleveland and Chicago areas as well as New York and Los Angeles.
The second is a tree that seems to have arisen in the middle Atlantic area in the 18th Century, with subsequent migrations to Pennsylvania, central Ohio (Mansfield area), and northern Indiana, e.g. Whitley County.
The third, and smallest is the one from which I am descended, may possibly be connected with # 2, above, has murky origins in 18th Century Maryland, but more provably settlement in northern Virginia, esp. Farquier County. There were 5 brothers, three spelling the name Tarman, and one Tearman. Their migrations in the early 19th Century included stops in Muskingum Co, Ohio and Brown Co. Ohio, and thence to Bartholomew and Johnson Counties, Indiana, and for two, later to Hancock County, Illinois. According to entries in the 1880s, the heritage was Scot-Irish. Subsequent descendants in Johnson County, Indiana, have included the Terman, Tearman, and Turman spellings.
James W. Terman