A library in Mercer County plans to upgrade its decades-old infrastructure after receiving a federal grant, local officials announced Tuesday. Hamilton Township was awarded nearly $1.6 million for public library improvements, officials said. The money will be used to replace deteriorating and broken windows, renovate bathrooms and upgrade the children’s area with new furniture, bookshelves and play areas, officials said. All of the windows, bathrooms and items from the children’s section are original to the building from the 1970s, library officials said. “Updating the library and other outdat…