621 17th Street, formerly known as the First Interstate Tower South, is a high-rise building in Denver, Colorado, United States.

It also stood as the tallest building in the city at the time of its 1957 completion, and held that distinction for eleven years until it was surpassed by the 420-foot (128 m) Brooks Towers in 1968.

[4] At the time of its completion, 621 17th Street was known as "First National Bank Building", its primary tenant.

[4] After First Interstate merged with Wells Fargo in 1996, the building's official name became its address.

[6] The building with the First of Denver logo can be seen in the opening credits of the television show Dynasty.