Townships are divided into two classes, depending on their population size and density. Townships of the "First Class" have a board made up of five to fifteen commissioners who are elected either at-large or for a particular ward to four-year terms, while those of the "Second Class" have a board of three to five supervisors who are elected at-large to six-year terms. Some townships have adopted a home rule charter which allows them to choose their form of government. One example is Upper Darby Township, in Delaware County, which has chosen to have a "mayor-council" system similar to that of a borough.