Reading about Slavery in British North America and then in the United States, I have read about maroon communities in the Great Dismal Swamp of Virginia, and also elsewhere in the South. Leaving aside Florida, which seems like its own case, just how stable and long-lasting were larger maroon communities in the Great Dismal Swamp and elsewhere?
You've really asked a tough one! Maroon colonies in South America and the Caribbean were more common and in many cases long-lasting, and as you've stated, Florida being a special case, the historical evidence for Maroon colonies in most places in North America is severely lacking. Most of what we do have comes from a singular perspective (white men, typically Wanted Ads) and scant archaeological evidence. Richard Price's 1979 seminal work Maroon Societies says this:
"It seems likely that about two thousand negroes, fugitives, or the descendants of fugitives, lived in this area. They carried on a regular, if illegal, trade with white people living on the borders of the swamp. Such settlements may have been more numerous than available evidence would indicate."
Much more relevant is Daniel Sayers' recently released A Desolate Place for a Defiant People: The Archaeology of Maroons, Indigenous Americans, and Enslaved Laborers in the Great Dismal Swamp. Sayers has been the foremost archaeologist of the Great Dismal Swamp Maroons since 2003 and believes that more than ten generations of Maroons, poor whites, Native Americans worked and lived in the Great Dismal Swamp from the late 1600s till 1865. He's found evidence of cabins, and what he believes to be an armory along with tobacco pipes, fire pits, lead fragments and other archaeological findings. While its impossible to know exactly how many Maroons lived in the Great Dismal Swamp, most scholars believed them to number in the hundreds, if not thousands and bear semi-continuous communities.
I would add to what has already been written by /u/dubstripsquads and /u/anoraklibrarian this that is not a phenomenon exclusive to the continental United States, as has been alluded to. Similar communities appear in the Caribbean and other parts of the New World also; perhaps most famously, to this day, there still exist three autonomous Maroon-descended communities in Jamaica, which have retained some elements of their 'original' culture; they are are for all intents and purposes regarded (at least officially) as an autonomous, indigenous people by the Jamaican government, distinct from the wider African Jamaican population.
Though the historical record is of course limited, these communities in Jamaica appear to have been very much autonomous and independent, not only of white society but of each other, with considerable stability and relative prosperity. Two broad , loose factional groupings can be identified based on geographical distribution but each individual community appears to have developed with relative autonomy (and I suspect these broad geographical classifications stem more from British conceptualisation of the 'Maroon problem' in the late 18th Century rather than any kind of meaningful political or social coalition); their long-term survival was made possible by skillful military resistance, command of local geography and quite possibly their disparate nature. In 1739, after decades on intermittent conflict with Maroon settlements and their fighters (Maroon oral tradition puts the span of continuous conflict at some 84 years), the British negotiated peace settlements with the various disparate communities and signed formal compacts of them (see here for a contemporary artistic representation of the signing), guaranteeing them their independence.
These compacts granted the Maroons autonomy over stretches of territory, hunting grounds and the right to self-defence, whilst accepting British legitimacy to govern and promising to protect British colonial assets in the event of foreign invasion of the island. The treaties also required the Maroon settlements to reject any escaping slaves and return them to the authorities - part of the rationale behind signing these compacts was to pacify what was seen as a substantial threat to the slave system. At least one Maroon group tried without success to revolt against perceived British violations of their compact at a later date but without success - and without support from other Maroon settlements.
Maroon tradition and oral history appears to reflect a culture that set itself apart from other African Jamaicans to some degree; though there was recognition of their common bond, the Maroons participated - reportedly with substantial brutality and even enthusiasm - in the extremely violent political repression that followed the 1865 Morant Bay uprising by African Jamaicans (and possibly some poor white people), acting at the behest of the Jamaican authorities, though there does appear to have been reluctance and conflict on the part of their leadership in participating in that bloody enterprise. Of course, such a distinction and rejection of common identity can also surely be framed consequence of or a reaction to an imperial 'divide and rule' policy adopted by the British authorities, rather than an authentic and organic deviation in social values.
Some reading recommendations:
It's worth noting that there were places like The Great Dismal Swamp in many local areas. Authors like Stephanie Camp and Anthony Kaye as well as contemporary slave narratives have noted that there were isolated places, often swamps or other wild lands that adjoined plantations that were used as places for regular runaways and that members of neighboring slave plantations would help provision. These weren't meant to be permanent escapes and enslaved people would return generally return after long absences, but these places were known and utilized by multiple enslaved people acting in autonomy.
The other communities that sort of make it into the maroon spectrum and that existed until the end of slavery are the tri-racial isolates of multiple states. Places like Mahwah, New Jersey home of the "Jackson Whites," or various Appalachian populations that were known as 'melungeons' developed as Native Americans, Europeans (often fugitive indentured servants) and enslaved Africans formed communities together in isolation.