This is a fun question. First thing to note is that newspapers were published by printers, and in the 1770s and 1780s, almost no printer devoted him or herself solely to their newspaper. The printer was also often publishing books, pamphlets, broadsides, and other printed texts, and sometimes selling them in the print shop. Newspapers printers were therefore not devoting most of their time and attention to gathering original information.

Instead, a printer in somewhere like Georgia would have relationships with newspaper printers across the continent, and perhaps across the Atlantic world. The printer of the Georgia Gazette might mail a copy of his paper to printers in Boston, New York, Philadelphia, Baltimore, and elsewhere, who would mail copies of their papers to Georgia. This was called the "exchange system." It allowed newspaper printers to gather intelligence, which they would usually reprint verbatim. That's one reason why if you look at these old newspapers, you'll find that they are divided into geographical sections, with headings like "London," "Paris," or "New-York." Grouping news by its place of origin was convenient for newspaper printers because they were often essentially copy-and-pasting news from other papers.

That would be the main source of information. There are two others. First, letters were frequently being exchanged across the continent. If a merchant in New York wrote a letter to a friend or business partner in Savannah, for example, the recipient might share a copy of the letter with local friends or with the newspaper printer. Printers regularly shared extracts from personal letters if they contained interesting tidbits. Unless a letter was specifically marked as private, there was an expectation that its contents could be shared beyond its recipient. The final source of information for a newspaper printer was, essentially, travelers. Someone who passed through a town might encounter a newspaper printer, or one of the printer's friends, and share accounts or rumors that would soon end up in print. Printers weren't very scrupulous about verifying this kind of thing, and often published false accounts.

You asked as well about how information exchanges changed for local events. 18th century newspapers didn't publish that much local news. Because they generally were published once or twice a week, by the time they go around to publishing, most members of the small communities they published for would have already heard about any local news. They might, however, insert accounts, letters, or reports at the request of some of their subscribers (that was one way of keeping subscribers happy) or of the political faction they were allied with. If a major event might be of interest to readers far away, someone aligned with the newspaper's political affiliation would probably write it up in a paragraph or two—probably exaggerating a few things to align with their Loyalist or Patriot commitments.

Your final question is about how much a local government controlled newspapers. Not as much as you might think. In the early 18th century, newspapers tended to be controlled by colonial governors and colonial governments. But in the American revolutionary era, many newspapers defied these restrictions and started publishing with the support of local political factions. Colonial governments avoided censoring or shutting down Patriot newspapers for fear of igniting a backlash. But Patriot committees, mobs, and eventually governments were more restrictive in places where they dominated. They shut down Loyalist presses, intimidated Loyalist printers, and sometimes physically attacked them.

Sources:

Robert G. Parkinson, The Common Cause: Creating Race and Nation in the American Revolution (Chapel Hill, 2016).

Joseph M. Adelman, Revolutionary Networks: The Business and Politics of Printing the News, 1763–1789 (Baltimore: Johns Hopkins University Press, 2019).