Industrial heyday towns.

[BigMattFromTexas]

What cities/towns were pretty big during the oil boom? I know Midland and Odessa, Tx were, San Angelo is kind of more recently drilling for oil. Also what other towns were bigger in their industrial(coal, gas, electricity?) Thurber, Tx was once the largest town between Dallas and El Paso, now it has a population of 8... Carlsbad was once a nice sized town outside of Angelo, it was home to the Carlsbad State Tubercular Sanitarium, now it's a small ghost town. I know of more but what local heyday towns do you know about?
BigMatt

[golden eagle]

A lot of northern rust belt cities like Flint and Detroit fit that bill. But as the American auto industry began its decline, so did those communities.

[PAHighways]

Pick any town in the Monongahela Valley:  Monessen, McKeesport, Duquesne, Rankin, Homestead, Braddock, etc. all based their economies on steel manufacturing.  While there are still US Steel facilities in Clairton, Braddock, and McKeesport, they aren't the major employers they were 50 years ago.

South of Interstate 70, coal was king in places such as Brownsville.

[Stephane Dumas]

Before asbestos was banned, the mining towns of Asbestos, Black Lake and Thetford Mines thrived with the asbestos mines in Quebec.

Schefferville and Gagnon was created as a response to iron mining in Quebec North Shore. Gagnon was completely razed while Schefferville still exist to desserve the surrounding Natives communities but recently there some plans to revive the mining exploration at Schefferville.

Trois-Rivieres and Shawinigan thrived with the paper and forest industry. They both currently try to diversifiate their local economies.

[Brandon]

Calumet, MI (and surrounding area) was near 100,000 during the copper mining era (ca. 1900) in the Keweenaw Peninsula.  The town itself is under 1,000 today, and Houghton County only has 35,000.