Just as I suspected, Portland, ME is named after the Isle of Portland in the English Channel, but that was a change from its original and much superior name Falmouth Neck. I would WAY rather our town have inherited the name Falmouth Neck, OR but what can you do.
The Isle of Portland is the Portland that started this whole mess, presumably named after the fact that there was a port there and it was some land. Fortunately, "Isle" didn't make the jump across the Atlantic, allowing future cities to have only two geographical words smashed together instead of three.
US cities aren't the only progeny of that Portland. Portland Stone is a kind of limestone mined from the Isle of Portland. Portland Cement, which is used in most concrete, is made from a different kind of limestone but was so named because it looked like Portland Stone. For the same reason, I would have named it Gray Cocaine Cement.
Portland, Victoria in Australia was NOT directly named after the Isle of Portland, but rather took its name from the middle man, 2-peat British prime minister the Duke of Portland.
The good news is we're the biggest (and best!) Portland in the world. Portland, ME has a metro population of half a million while Portland, Victoria and the original Isle of Portland have only 22k people between them. The Duke of Portland had a population of 1.
It's too bad we don't get to do much city naming anymore. But if we did, I think we've learned enough to not name cities after other cities. Cements and dukes, go for it.
Update: Other Portlands
Obviously this list wasn't exhaustive, just my favorite Portlands. There are 20+ other cities named Portland around the world. Some other notables:
* Portland, TX (Named after Portland, ME. Includes #73 on the Great Texas Coastal Birding Trail!)
* New Portland, ME (Oh shit! I hope old Portland, ME doesn't find out they've been replaced)
* Portland Parish, Jamaica (A leading producer of breadfruit, which is totally a thing)
* Portland Street, Hong Kong (famous for it's red light district, but in China red lights just mean communism)