This interesting and unusual surname, chiefly found in the north western European countries of Denmark, Holland, Germany and Brussels, and also further north in Finland, is a patronymic from the male given name Peter, itself ultimately coming from the Greek petros, meaning "rock" or "stone". Recordings of the surname from London church registers include the christening of Frederick Beltezer, son of Otho and Catharine Petersen, on April 9th 1706 in St. Martin in the Fields, Westminster; the marriage of Joachim Petersen to Elizabeth Spofford in St. Dunstans in the East on August 12th 1712, and the christening of Adolph Frederick Petersen in St. Botolph without Aldgate on September 1st 1872. Coats of Arms granted to the Petersen families of Greiffenberg, (Prussia); Hesse, and Finland are recorded heraldically in Rietstap's "Armorial General", the former depicts the upper body of a stag leaping from the centre of a blue shield. A silver cross moline is the base. The first recorded spelling of the family name is shown to be that of Petersen of Prussia, which was dated circa 1680, Rietstap's "Armorial General", during the reign of Emperor Leopold 1, "Habsburg Emperor", 1658 - 1705. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.
http://www.surnamedb.com/Surname/petersen#ixzz2mA54YUUJ
Danish, Dutch, Norweigan, & North German patronymic form of Peter.