Trenčín flourished again during the era of the first Czechoslovak republic and became the capital of the Trenčín county again between 1940–1945 when the Slovak Republic was in existence.
Trenčín berkembang lagi dalam masa pemerintahan Republik Cekoslowakia yang pertama dan menjadi ibu kota County Trenčín lagi antara 1940–1945 ketika Republik "boneka" Slowakia berdiri.