Jacobus is a borough in York County, Pennsylvania, United States. The population was 1,841 at the 2010 census.
Founded in 1837, Jacobus was originally called New Paradise. The name was later changed because of misdelivered mail between New Paradise and the town of Paradise, Pennsylvania in neighboring Lancaster County.
The name Jacobus (jă-KŌ-bŭs) was derived from the name of the town's postmaster, Jacob Geiselman (1829-1909). To correct the problem of the misdelivered mail, the United States Post Office Department notified Geiselman to change the name of the post office. However, Geiselman was unable to think of another name. Therefore, the mail was sorted and forwarded to Geiselman labeled as,"Jacob-US Mail;" which was later shortened to "Jacob-US." The post office was then renamed Jacobus, and the town was renamed accordingly. In 1929, Jacobus became an incorporated Borough under Pennsylvania law. see Borough (Pennsylvania).
Jacobus is located at 39°52′57″N 76°42′43″W (39.882516, -76.712068).
According to the United States Census Bureau, the borough has a total area of 0.9 square miles (2.3 km2), all of it land.