M.J. O'Connor was born in London, England on March 27, 1833. He immigrated with his parents to America in 1836, and received his education in New York City. He removed to Chicago in 1848, came to Minnesota in 1855, and opened a gent's furnishing establishment on Third street.

He was a member of the common council from 1859 to 1862, refusing to be a candidate for re-election, but responded to the president's call for troops, and recruited for the Tenth Regiment, Minnesota Volunteers. He was chosen captain of Company K, and took part in General Sibley's campaign in fighting and driving the Sioux Indians across the Missouri River. O'Connor went south with his regiment in 1863; was appointed inspector general Department of the Missouri, and saw hard service while on inspecting tours, riding through southwestern Missouri.

In 1864 his regiment was attached to the Sixteenth Army Corps and took part in the engagement at Tupelo, Miss., routing the combined forces of Forrest and Chalmers. He served under Gen. A. J. Smith during part of thesummer of 1864, and took part in several minor engagements. He was with the Tenth and a picked corps under Gen. Joe Mower, who were ordered to follow the confederate General Price, and encountered one of the most severe campaigns of the war, marching thirty consecutive days through Arkansas and Missouri, which terminated in the fight on the Little and Big Blue Rivers, at which Marmaduke and a large force was captured and Price finally driven from that section of the country.

On the return of the Union forces south, Captain O'Connor was left in the hospital in St. Louis. but recovered in time to join his command at Vicksburg, and took part in the twenty days' siege of Spanish Fort and final capture of Mobile, this being about the last battle of the war. He returned home with his regiment, having seen service from our northwestern boundary at Devil's Lake and the Missouri River, thence southward to the gulf. He was mastered out at Fort Snelling in 1865.

The following fall O'Connor was elected city treasurer, which position he left to go into business with his brother, where he continued until 1870, when he was elected city clerk, which office he filled until 1879. He then formed a partnership and built the Northwestern Stock Yards, in which business he remained for a number of years.

In 1885 he was appointed by President Cleveland to be Appraiser of Customs for Minnesota. He is a member of the G. A. R.

In 1855 he married Miss Mary Fitzpatrick at Chicago, Illinois. She was the daughter of Doctor Walter Fitzpatrick, Queens County, Ireland. She made a most amiable wife and mother. She died in November, 1897, leaving her husband and four sons and two daughters to mourn her loss.