The site chosen for Ladd Observatory was at the top of the highest hill in the city of Providence. The hill lost that distinction in 1919.
The borders of Providence have changed a number of times. The settlement of Silver Lake was originally part of Providence, but the residents decided that this agricultural community had more in common with rural Johnston and choose to secede in 1759.
Expansion of the textile mills along the Woonasquatucket River in the mid 1800s led to demand for increased housing nearby. Silver Lake rapidly changed from rural to urban. In 1898 Providence annexed Silver Lake and western Olneyville. Providence expanded again in 1919 to include Neutaconkanut Hill Park. The portion of the hill still in Johnston is taller, but the part within Providence includes a summit at 259 feet above sea level. The elevation of Ladd Observatory is 205 feet.