Looking on the internet deeply has found these results:

on the factory is the most popular phrase on the web.

At the factory 147,500,000 results on the web	on the factory 160,400,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Well... at the factory, we work assembly lines. He works at the factory at this time. Preliminary soil analysis indicates those elements are not present at the factory. He's been a prisoner at the factory for months. This is the same stuff we saw at the factory. A body's been found at the factory. Frost killed Eustace Kendrick at the factory. There's another girl at the factory, same predicament.	The strike on the factory was unsuccessful. If she hasn't made contact by nightfall, I suggest a massive frontal assault on the factory, Madame. That's why you put a timer on the factory bomb. Tell the major we're sending in all of our sharpshooters... to support the attack on the factory. The whole place depended on the factory that closed. But I wouldn't have taken our only transportation to do it, and I wouldn't have stopped the assault on the factory. What do we tell people who have staked their careers on the factory, on production? ...on the factory, on production?

At the factory

147,500,000 results on the web

on the factory

160,400,000 results on the web

More popular!

Well... at the factory, we work assembly lines.
He works at the factory at this time.
Preliminary soil analysis indicates those elements are not present at the factory.
He's been a prisoner at the factory for months.
This is the same stuff we saw at the factory.
A body's been found at the factory.
Frost killed Eustace Kendrick at the factory.
There's another girl at the factory, same predicament.

The strike on the factory was unsuccessful.
If she hasn't made contact by nightfall, I suggest a massive frontal assault on the factory, Madame.
That's why you put a timer on the factory bomb.
Tell the major we're sending in all of our sharpshooters... to support the attack on the factory.
The whole place depended on the factory that closed.
But I wouldn't have taken our only transportation to do it, and I wouldn't have stopped the assault on the factory.
What do we tell people who have staked their careers on the factory, on production?
...on the factory, on production?