"first formed" is correct and usable in written English.
You can use it to refer to things that have been established for a period of time. For example, "The organization was first formed over 65 years ago."
A lot has changed for electropop trio Ekkoes since they first formed.
It's hard to say when the principles behind this art for contemplation were first formed.
He first formed a city commission to recommend the change in 2002.
Plans were first formed in the 1920s and have been periodically revived and abandoned.
That is when Patchogue first formed a library association, the third in Suffolk County.
He was part of the Chicago Symphony Chorus when it was first formed by Margaret Hillis.
The SAS was first formed in North Africa in July 1941, during World War II.
The other was that the Malayan field rat wasn't on the islands when they first formed.
His mature bronzes were often first formed in clay and then cast in monumental size.
Political parties were first formed in 1946, when a territorial assembly was established.
Loan recipients are first formed into groups, with repayments then the collective responsibility of all group members.
