Horsham Township is named after the town of Horsham in Sussex in the South of England. Horsham is one of several townships in Montgomery County whose name and size were determined by master survey lines drawn by William Penn's engineers as they first plotted this part of the colony for sale and settlement. Parallel lines, projected at intervals of a mile and a half and extending in a northwesterly direction from settlements along the Delaware, served not only as base lines for measurement of individual land grants but also as courses for future highways. County Line Road, Horsham Road, and Welsh Road are examples of highways so laid out. The effect of these survey lines upon the development pattern of Eastern Montgomery County is very much in evidence today.
In 1684, the entire township of 17 square miles (44 km2) was made available to individual purchasers. Samuel Carpenter, from the town of Horsham in Sussex, England, after which the township is named, purchased 5,000 acres (20 km2), 4,200 acres (17 km2) within the present boundaries of the township. In 1709, Carpenter, then Treasurer of Pennsylvania, began to sell tracts of land to migrating Quakers. In 1717, Horsham Township was established as a municipal entity by a vote of the people.
In 1718, Sir William Keith, then Provincial Governor of Pennsylvania, acquired 1,200 acres (4.9 km2) of Carpenter's land on which he erected a house in keeping with the dignity of his office. The development of Keith's "plantation" proved to be a step in establishing closer ties between Horsham and neighboring communities, particularly those of Hatboro and Willow Grove. He was responsible for the construction of the present Easton Road (PA Highway 611) from the old York Road junction at Willow Grove to his mansion on County Line Road in 1722.
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