John arrived in Chicago in 1836 and bought 40 acres for a farm in 1837 on Sunnyside Avenue near Philip Rogers' initial land holdings. O'Leary lived there from 1837 until 1840 when he bought 160 acres in Ridgeville that was north and east of Rogers' land.
While living in Ridgeville many of those who settled at Evanston passed their house in teams. They stopped and made their acquaintances; and when the O'Learys themselves moved to Evanston they found these acquaintances settled on various farms. Among them were Edward Murphy, John Carney, Hathaway and others.
In 1837 John O'Leary bought 160 acres in Ridgeville (situated in part where Calvary Cemetery now is) and in part south of the Cemetery and north of the present Chicago city limits. In 1840 he moved to Ridgeville. In 1859 he sold 40 acres to Calvary Cemetery, this being the year the Cemetery was established.
In 1850, O'Leary decided to go to California to seek his fortune in the Gold Rush. He returned in 1852 after some success. His grandson, David Philip O'Leary reported that John had made more than $2,500.
John had a daughter, Ellen O'Leary.