Dennis was born in 1833 in Ireland to unknown first name Haggerty and Mary Finucane. His mother married John Fitzgibbons in 1845 in Limerick, Ireland and the family was next found in the 1850 Census for Fall River, Massachusetts. A half-sister to Denny was born in 1846 in Fall River, so they must have arrived there between October 1845 and June 1846.
The family was in Marshall County, Illinois by 1855. Denny was listed in the 1860 Census as "Dennis Fitzgibbon", living with his step-father, mother and siblings. Dennis was Naturalized in October of 1860. In about 1861, Dennis married Margaret O'Brien. From 1864 to 1878, Dennis and Margaret had six known children.
In August of 1876 "A terrible tragedy was enacted at Lacon, about nine o'clock Tuesday night, the results of which will probably occasion the death of three men, who were fired upon by a mob of six men, through a window, all armed with guns or revolvers, all desperate characters, and who had gone there to do deadly work, regardless of consequences".
Backstory: there was a "...one room house, kept by a Mrs. Locke, a woman of easy virtue." A man had attempted to enter the house, but the house was full of other visitors, so he was turned away. He refused to leave, so Mrs. Locke shot at him. On the fatal night, an "attacking party" of Dennis Haggerty and five others came and demanded those in the house to come out (there were 7 people in the house), but before they could, firing began. It appeared that Dennis Haggerty was the leader of the "riot". It was also later reported that it was not six men who went to the one-story house that night, but that there was a crowd of 30 or 40 men and boys.
It was also reported: "that Haggerty ordered them to leave the house in two minutes, and within a minute, two or three shots were fired in at the window, and were immediately followed by a volley from the remainder of the guns."
Some of the men "gave a tacit approval of the plan of 'cleaning them out' as it was expressed." Three men were arrested (including Dennis). "The parties arrested show no signs of remorse for this dastardly work, but boast that they meant to do it and were not ashamed of it."
Bail was set at $8000 for Dennis, $2000 for Thad Power, and $1500 for Charles O'Hare. "O'Hara was immediately bailed out as he is generally believed to be innocent of any criminal intent in joining the mob." One man, Robert Iliff, died within a month or so from the attack.
It ended up that Dennis and two other men were put on trial for murder and were found not guilty. However, the newspaper articles (found in the below link), stated that some of the jury got out of town immediately following the verdict as they did not feel safe. The article also stated "Had not the witness Reddan Ames (who turned states evidence), been so anxious to appear 'smart' upon the witness stand, his testimony would not have been utterly disregarded by the jury as it was. Had he given his testimony in a straight forward manner, the jury, with ever so strong prejudices, could not have avoided finding a verdict of guilty against at least one of the defendants."
Link for the newspaper items: http://genealogytrails.com/ill/marshall/1876LaconShooting.htm
Dennis lived until December of 1889, when he died at the age of 56. I found this to be an interesting obituary for him:
from Marshall County Democrat, Lacon, IL, Friday Morning, Dec. 20, 1889:
"Denny Haggerty, well known in this community for the past fifteen years, died at his home on Wednesday night at about 11 o'clock. His disease seems to be a mystery to everybody but the doctors. He seems to have been taken with rheumatism or neuralgia and this seems to have settled about the brain. The doctors thought there might be something of a scum over the brain or some decay incident to some old contusion. Any way he has lain for some weeks a very sick man and death must have been a relief to both him and his family. Denny was esteemed a very rough man, but he had many good points A lack of education was his greatest drawback. He had the energy, the sense and the method to get on in the world. His will power was immense, and when he set himself to do or not to do, he brooked no opposition. This got him into a good deal of trouble and made him appear to disadvantage. Many men occupying 'front seats in the synagogue' are not as honest in purpose as Denny Haggerty. The funeral will take place at 10 o'clock this morning."
I think that Dennis qualified as a bit of a black sheep!