There are over 500 Henwoods listed on Facebook. It would be interesting if they were all related. Being that there is a village in Cornwall, England called "Henwood", it could be that the citizens took on the name as their surname. They could have started as a family unit that became a tribal unit, and then a village with some unrelated people living there that also took the surname. DNA would answer that question.
Think of how many Henwoods there are that are not on facebook. It's quite a popular name.
There are 3,687,503 entries of Henwood on www.ancestry.com. I see that Henwood has been in the USA for a long time, even back in Indian wars.
Move over, Smith and Jones. Henwood is a popular name, also.
Reference: Facebook, www.ancestry.com