[23] Allen was an important man in Buffalo, and he introduced his nephew-in-law to influential men there, including the partners in the law firm of Rogers, Bowen, and Rogers.[24] Millard Fillmore, the 13th president of the United States, had previously worked for the partnership.[25] Cleveland later took a clerkship with the firm, began to read the law with them, and was admitted to the New York bar in 1859.[26]

Early career and the Civil War
Cleveland worked for the Rogers firm for three years before leaving in 1862 to start his own practice.[27] In January 1863, he was appointed assistant district attorney of Erie County.[28] With the American Civil War raging, Congress passed the Conscription Act of 1863, requiring able-bodied men to serve in the army if called upon, or else to hire a substitute.[26] Cleveland chose the latter course, paying $150 (equivalent to $3,301 in 2021) to George Benninsky, a thirty-two-year-old Polish immigrant, to serve in his place.[29] Benninsky survived the war.[26]
As a lawyer, Cleveland became known for his single-minded concentration and dedication to hard work.