Hashish was known in the West as early as 1596, when it was described by Jan Huyghen van Linschoten in a book describing his travels in Egypt and Turkey. But it wasn't until the 19th century that smoking cannabis became widely known in the West, through portrayals of oriental exoticism by writers such as Dumas.
Hemp was grown in the British colonies starting around 1619 in order to make rope, which was in demand by the British Navy. Today, industrial hemp has a low level of THC and a high level of CBD. Because CBD suppresses the narcotic effect of THC, this combination makes it impossible to get high by smoking industrial hemp, even if you puff up a storm. We don't know if 18th-century strains were similar to modern industrial hemp, but there is no hard evidence that they were any different.
A lot of people in the marijuana legalization movement, as well as a lot of people who would like to legalize cultivation of industrial hemp, want to believe that Washington, Jefferson, Franklin, et al. smoked hemp in order to get stoned, because this might help to legitimize pot. (Never mind that some of these guys also owned slaves...does that make slavery OK?) But their evidence is pretty weak. There seem to be a lot of fabricated quotes running around, as well as some quotes that you really have to stretch in order to construe them as evidence that the founders got high on hemp. It's known that hemp was considered a form of medicine in that period, but lots of herbs are considered to be remedies without actually getting anyone high.
The word "marihuana" didn't become current in the U.S. until about 1900, when the drug was commonly used by Mexican immigrants and started to become common in subcultures such as jazz musicians. There is no real evidence that before that time, it was common for people to grow Cannabis in the U.S. that was capable of getting anyone high. Although it's true that marijuana had a much lower THC content back in the 60's than it does today, that doesn't mean that the stuff back then was equivalent to industrial hemp; it had more THC and less CBD than industrial hemp.