There are a number of chemical elements that are named after towns, including strontium, dubnium, berkelium, darmstadtium and hassium. There are actually four elements that get their name from the town of Ytterby, Sweden: ytterbium, erbium, terbium and yttrium.
Strontium gets its name from the town of Strontium, Scotland, while dubnium is named for the Russian town of Dubna. Berkelium was first discovered at the University of California at Berkeley and takes its name from that city. Darmstadium and hassium were named after the German towns of Darmstadt and Hesse, respectively.
The reason that so many elements are named after Ytterby, a tiny island off the coast of Stockholm, is due to the presence of a rare earth mine on the island. Rare earth elements tend to become mixed up in the ground, so many are usually discovered at one time. In fact, seven total elements were discovered at Ytterby, but only four directly took their name from it.
The other three elements are holmium, thulium and gadolinium. Thulium takes its name from an ancient word for Scandinavia, while gadolinium is named after the person who made the original discovery, Josh Gadolin. The name holmium comes from the Latin word for Stockholm, Holmia. This is similar to the element hafnium, which comes from Hafnia, the Latin word for Copenhagen.