Longyear was born on October 22, 1820, in Shandaken, New York,[1] the son of Petrus Longyear (also known as Peter Longyear, 1784–1845), of Dutch heritage, and Jerusha Longyear (née Jerusha Stevens), of English heritage.[2] The Longyears were descendants of Jacob Longyear Sr. (also known as Jacob Langjaer), an 18th-century immigrant to New York from Holland.[3] Longyear pursued classical studies at the Lima Academy in New York.[4] He taught school for several years in New York.[4] He moved to Mason, Ingham County, Michigan in 1844 and taught school.[4] He read law and was admitted to the Ingham County bar in 1846.[1] He entered private practice in Mason from 1846 to 1847.[1] He continued private practice in Lansing, Michigan from 1847 to 1870.[1]