On October 10, 1750, in Lancaster County, Pennsylvania, there is a warrant (#566) to William McFarlin, for 172 acres in Earl Township, and again, in 1756, for 100 acres (NGSQ 21:1-13), however this may not be the same William.
In August of 1786, in Greene County, Tennessee, the Common Pleas records list a Justice William McFarland (page 66), and in May 1787, the records list oaths of William McFarland Esq., & James McFarland, that they each attended court 8 days as witnesses in Joe Baits vs James King (page 77). On March 25, 1788, in Greene County, Tennessee, the Tennessee Deed records list William McFarland as a witness to a sale from Alexander Outlaw to John McFarland, for 200 acres on north side of Nolachucky (Book 3, page 107). On October 15, 1788, in Greene County, Tennessee, he is listed as bondsman along with a John McFarland for the marriage between Ewen Morgan ans Abigail Netherton.
He was living in Greene County, Tennessee, in 1790.

William McFarland married Elizabeth Kirkpatrick about 1760 in probably Cumberland County, Pennsylvania. They had the following children, all born in Cumberland County, Pennsylvania:

Joseph (4 Feb 1761 - 3 Nov 1839) m. Margaret White
William (3 Apr 1763 - 1 Sep 1816) m. Rebecca Kirkpatrick
Margaret Rebecca "Peggy" (1764 - 1822) m. Nathaniel White
Benjamin (1765 - ) m. Martha Stevenson
Nancy (abt 1775 - aft 1830) m. George Taylor