Oscar was the oldest son of Frederick and Rebecca McIntosh. He was born in Kentucky, perhaps in Bath County where his parents were married. Or possibly in Greenup County like the family's next child was.

He married Martha Sappington on Feb. 15, 1846 in Kentucky. Martha was born Aug. 29, 1829. He and his extended family traveled overland to California, arriving in July, 1852.

Their youngest child, Oscar, Jr., died in September, 1852, not long after they arrived in California. Oscar died soon after his son, in October, 1852. His wife Martha may also have died that same year. But other records say that Martha died Jan. 2, 1874, in San Leandro, Alameda County, Calif.