で働いてたんだ

was working at

→ で

phrase Rare #37,772

was working at A casual form of で働いていたんだ. The んだ adds an explanatory or emphatic tone, often conveying “you see” or giving background information. The place or organization comes before で.

JA: 姉は去年、東京の病院で働いてたんだ。

EN: My older sister was working at a hospital in Tokyo last year.

トムはボストンで働いてたんだ。

Tom worked in Boston.

信じられないどころか私はホーム・デポの店長だがあのサイコはウチで働いてたんだ

You’ll never believe this—I’m the manager at Home Depot, and that psycho used to work for us.

— 人生スイッチ (2014)

僕はそこで働いてたんだ。

I used to work there.

徹夜で働いてたんだ。

I worked all night.