What is the opposite of municipal annexation, and when does it happen?

Cities and other municipalities will sometimes annex nearby territory. There are a variety of reasons for this that we could discuss elsewhere if folks are interested.

Do cities (or other municipalities) ever divest themselves of territory? If so, what is it called, and how does it occur? I’m talking about situations other than when a municipality completely disincorporates.

Yes, I have seen it happen. Chebeague Island, Maine - Wikipedia
I think this scenario is fairly common. An island community does not agree with the mainland town that owns it, and secedes.
Chebeague isn’t even the first island in Casco Bay to do this.
Long Island, Maine - Wikipedia

There’s a small movement of malcontents in Staten Island who keep trying to secede from New York City. Thus far they have been unsuccessful. But other places have managed to do it.

In Detroit the term usually used in the media discussing this was unincorporation. There was talk about doing this with some of the outlying less populous areas that didn’t bring in many tax dollars to reduce the costs of providing services.

From what I’ve seen & heard about Staten Island, I get the impression that it’s much more suburban than any other borough of NYC. Actually, if you look at a map, it would make more sense for Staten Island to be part of New Jersey than anywhere in New York.

I think the proposal to unicorporate parts of Detroit has fizzled out. There are plans to clear out neighborhoods that are mostly abandoned, but these neighborhoods don’t form a contiguous block of territory which would lend itself to unincorporation.

Deannexation, as in Georgia or Tennessee.

A New York Times employee once said that Staten Island leaving New York would be like Gummo leaving the Marx Brothers.

The last time it happened around here was 2011, when the 1,337 residents of St. George, Mo. voted to disincorporate.

St. Louis city voted to secede from St. Louis County in 1876, if that counts.

In Ohio it’s called detachment. But it can’t be initiated by the municipality, just the property owners, AFAIK. In some cases the municipality has to consent, though.

Deannexation typically happens when the city decides it doesn’t want the territory after all. A good example would be 300 acres annexed in anticipation of some big factory or residential development that ends up not occurring. The city doesn’t want to be required to provide services to the area without the property tax revenue it anticipated from the big development, so the territory is deannexed.

Sometimes an annexation is ruled improper by a court, requiring the deannexation. A famous example would be Chicago’s first attempt to bring O’Hare Airport into the city by using a strip along Higgins Road. A state court ruled that wasn’t sufficient, so a much wider strip was arranged by trading territory with the Village of Rosemont.

Likewise, there is a perennial movement in the San Fernando Valley to detach from Los Angeles and become a separate city (or several). (Note, there are several areas in the Valley that already are and always have been separate cities.) This never goes anywhere.

Thanks folks. To summarize, we have:

Secession
Unincorporation*
Disincorporation*
Detachment
Deanexation
*Also used to describe complete dissolution of a municipality.

Happens quite often when national borders are redrawn following a war. Prominent examples off the top of my head include East/West Berlin, Komárno/Komárom, Frankfurt an der Oder/Słubice, and Görlitz/Zgorzelec.

The old speed trap of Hampton, Florida annexed a stretch of county road 301 back in the early 90s to establish their speed trap. After rampant corruption was uncovered in town, mostly from the revenue from the speed trap, the city was almost forced to unincorporate by the state. They were allowed to stay incorporated, but they retracted their annexation of the stretch of county road 301 and their police force was decommissioned.

One very interesting case like this that I know of that was partially successful was the Montreal merger/demerger issue of about ten years ago.

In 2002 all the smaller municipalities of the island of Montreal were annexed to the city of Montreal by force from the government of Quebec.

Many of the people of the people of those smaller towns were very much against this forced merger, and in 2003 a new provincial government was elected which promised to undo the mergers under certain conditions.

In 2006 those conditions had been met in many of those towns, and they split off to become separate municpalities again.

The return of the Virginia portion of the District of Columbia was called “retrocession,” but I don’t believe the term applies to what the OP is asking.

One of the links at the end of that Wiki article mentions other cities that did similar, including one city in Ohio that actually was dissolved.

Oh, I see that as usual Wikipedia’s already got a list for this: List of divided cities

So essentially it looks like 2 main methods:

  1. A city annexes some uninhabited land, and then later divests itself of the land.

  2. Part of a city decides that it doesn’t want to be part of the larger city, and initiates some kind of divestiture proceedings to become its own municipality, with some sort of referendum and consent of the larger city.

I can’t really see any other options, otherwise we’d have seen cities divesting themselves of low-income and/or problematic sections for decades, and we haven’t seen that.