In the nid-1970s when I was finishing my PhD diss and also working for the Wisconsin Department of Natural Resources in its Water Quality Bureau, where I was mostly dealing with sewer systems issues, the Wisconsin branch of the Posse Comitatus was attacking and "arresting" individuals from my department who were trying to enforce limits on fishing of certain fish in certain lakes in Northern Wisconsin, some of these involving local Native American rights to fish some of these species in these lakes.
In 1878, just after President Hayes removed most of the Union troops from the South at the end of Reconstruction, Congress passed the Posse Comitatus Act, which put limits on the federal government dominating local government authorities. Not sure when the Posse Comitatus movement got going, but they were there in Wisconsin in the mid-1970s, The last time this decentralized group got attention was in 2012 when some of their followers were arrested for physically attacking some people.
But, while they may still exist in some shadow form, they have been clearly replaced by an organization formed in 2011, give or take a year, the Constitutional Sheriffs and Peace Officers Association (CSPOA). This group, with links to such far right wing groups as Oath Keepers, apparently has 10% of US sheriffs as members.
A fundamental point that both the older Posse Comitatus group, and this newer CSPOA group share, drawing on an extremist interpretation of the Jim Crow 1878 act, is that Sheriffs are the highest level of legal government. The federal and state governments are illegitimate and irrelevant. So, when a Sheriff arrests a Wisconsin Department of Natural Resources officer trying to enforce state rules on how many fish can be caught in a particular lake, well, they have no authority, and the local Sheriff can arrest them, and they did, even as, unsurprisingly, courts did not support their views of such matters.
There is a sharp contrast between county Sheriffs and city police chiefs. The former are usually elected, and have an average tenure of 11 years, with some states putting no limits on their campaign financing. Jefferson Parish in Louisiana Sheriff, Harry Lee, who held his position for over 30 years, declared (according to WaPo, 11/2/21) that he was "the closest thing to being to being a king in the U.S." OTOH, police chiefs are appointed, and their average tenure is a mere 3 years.
He is now out of power, and not in jail because Donald Trump pardoned him, is Joe Arpaio, former longtime Sheriff of Maricopa County in Arizona, which includes the now fifth largest city in the US, Phoenix. He was in office from 1993 to 2017. He eventually got into legal trouble for the camps he interned illegal immigrants in, widely described as being "concentration camps." Yes, these Sheriffs have great power. But then he supported Trump's old lie that Obsma was not born in the US. He still holds that view, and Trump pardoned him.
Bottom line here is that now these people are calling themselves "Constitutional Sheriffs," and some of them participated in the 1/6/21 insurrection. They view themselves as superior to both state and fedreal governments, and they increasingly support far right views of the world.