Hitherto, Mr. Dearborn, while entertaining positive views, had not actively participated in political discussion. But the year 1856 witnessed the consolidation of the anti-slavery sentiment of the country. It had already so far concentrated its strength in New Hampshire as to have secured the state government and a unanimous representation in Congress. The nomination of John C. Fremont for president, in the summer of that year, hastened the organization of the anti-slavery elements of the entire North under the name of the Republican party. In common with a majority of the intelligent young men of the state, Mr. Dearborn entered into this contest with all the zeal, vigor, and enthusiasm of one whose action is untrammeled by personal or partisan ends. The campaign which followed was the most brilliant and far-reaching in its results of any in the political history of the nation. No idea ever agitated the American mind to which calculating selfishness was more foreign. Even the great uprising which brought about the war of Independence was less free from selfish motives. And, though the general result in the presidential election of that year was adverse, yet in New Hampshire, as in every state north of Pennsylvania, the returns clearly showed that the cause of freedom had acquired an over-ruling strength. In June, 1857, Mr. Dearborn was united in marriage with Miss Louie Frances Eaton, daughter of Moses W. Eaton, of Francestown, and grand-daughter of Dr. Thomas Eaton, a physician of long and extensive practice, and one of the most enterprising farmers of his time. In 1857 he was elected county treasurer, and re-elected in 1858. It was the first public position he had held, and its duties were satisfactorily discharged. In 1858 he removed to Peterborough, occupying the office of E. S. Cutter, Esq., who had recently been appointed clerk of the courts for Hillsborough county. He resided in Peterborough till 1865. During this time he was in partnership with Charles G. Cheney, and afterwards with Albert S. Scott, both of whom have since died. He represented the town in the legislature in the years 1861 and 1862, being a member of the judiciary committee.