According to the United States Census Bureau, the borough has a total area of , of which , or 1.45%, are water. Denver sits in a valley formed by Cocalico Creek to the west and Little Cocalico Creek to the east; the two creeks join at the southern border of the borough. Cocalico Creek is a tributary of the Conestoga River and part of the Susquehanna watershed.
According to the United States Census Bureau, the borough has a total area of , of which , or 1.45% are water. Denver sits in a valley formed by Cocalico Creek to the west and Little Cocalico Creek to the east; the two creeks join at the southern border of the borough. Cocalico Creek is a tributary of the Conestoga River and part of the Susquehanna watershed.