This is the 1820 New York census for Allegany County, NY, in the town of Pike, and shows a William Holley as a resident. The land here opened up for sale in 1816.  Since there were no William Holley's living in Allegany County in 1810, then this  probably means that William Holley moved to Allegany County, NY, between 1816 and 1820. 
     Daniel Hawley's (great-great-great grampa) death certificate states that his father was William, and according to the 1845 and 1850 censuses, Daniel claimed to have lived in Allegany County well before 1820.  These two pieces of evidence suggests that the William Holley shown on this 1820 census could be Daniel Hawley's father.

This comes from a history book on Allegany, NY, and is in the section, "Early Settlers in Hume".  This is the same location where William Holley lived.  This document claims that a "blank" Hawley lived here before 1819.  The only Hawley/Holley living in this area at that time was William Holley, so I think they are the same person.

This document shows that the land came into market around 1816.  Increase Hawley is mentioned, but he was not in the 1820 census.  He was in the 1830 census with his father, Nathan.  Increase was born in Orange County, NY., and is directly connected with John Holly, who came to America in 1630.