Here are some words that are made plural in the same way, by adding "-ies" to the singular form:
* Country - Countries
* Baby - Babies
* Berry - Berries
* Cherry - Cherries
* Company - Companies
* County - Counties
* Story - Stories
* Factory - Factories
* Library - Libraries
* Party - Parties
* Activity - Activities
This pattern is common for words ending in "-y" preceded by a consonant.