The US employed lots of surveyors. As the government moved west, so did the surveyors. It was an important government (and private) job and the law for it dates back to the 1780s - it was passed by the Continental Congress before the revolutionary war had even ended.

They developed a plan on how to survey the Northwest Territories (which stretches from Ohio to Minnesota). The US created a government post of the Surveyor General of the Northwest Territories in the 1790s. They were responsible for setting markers and would go out west with lots of survey equipment and lay down where all the key points are. There are a ton of "County Line Road" roads out west because the road would end up following the surveyor line.

Before this was systematically laid out, surveys would be based on natural features, like "from the large bend in the stream 1/2 mile from the junction with the Big River, 400 yards to the large, solitary walnut tree." But that's not a great system, as rivers move, things erode, trees die, etc.