The Journal of the Assembly gives the totals as 52,497 for Chellis, 34,479 for Irwin, and 32,356 for O'Farrell.
Candidates party affiliations obtained from the 9/7/1861 Sacramento Daily Union. https://cdnc.ucr.edu/?a=d&d=SDU18610907.2.2&e=-------en--20--1--txt-txIN--------
Source for Popular Vote data: California State Archives, "For Lieutenant Governor," Statement of the Votes Polled at a General Election Held in the State of California on the Fourth Day of September A.D. 1861 (Sacramento, 1861)