He said that a third were Patriots, a third were Tories, and a third were neutral.

In the letter when he wrote that, he was talking about American support for the French Revolution during the late 1790s--twenty years after the US revolution. Far more than 33% of colonists supported the Revolution--and once the war broke out certainly more than 33% were neutral about its outcome. The American Revolution was the bloodiest in terms of per capita casualties. 25,000 military deaths and thousands more of uncounted civilian deaths out of a population of 2.5 million.

A similarly proportioned fight scaled on today's population would be a war with three million military deaths--or a conflict nine times more deadly for Americans that all of World War Two. So, no, one third of Americans did not stay neutral on the US Revolution.

I'm not sure anyone is really in a position to state what the majority opinion was across the country. Even by April of 1775, when the conflict begins, Virginia among others questioned whether to get involved in what they saw as pretty much of a New England conflict. Concord and Lexington were really part of a series of incidents in the northern colonies where the people were objecting violently to the attempts by the parliment and the crown to assert authority. The troops were occupying Boston for a reason, and those reasons didn't particularly exist in Virginia.

I'm fairly sure that within the merchant class, there was a high level of support for revolution. For much of the agrarian class I'm not really sure we can tell. Ignorance may have been the most common situation.