Dennis Barry Haggerty (born Denis Hegarty) was born in County Cork, Ireland on March 3, 1824 to Denis Hegarty Jr. (1795-1865) and Mary Barry (1803-1856). He grew up in Ballyhoulahan, a homestead near Rosscarbery, on the southern Irish coast, in a household with 10 siblings.

Denis emigrated from Ireland to Louisiana at the young age of 10 to work with his uncle (on the Barry side of the family) on a plantation in "Bayou Teche County" as a planter. Later he worked as a drayman, guiding river transport boats with horses. Meanwhile, two of Denis’ sisters moved to New Orleans as nuns at the Marianites of Holy Cross mission to serve the growing Irish Catholic community. Denis moved from Bayou Teche County to New Orleans around 1850 to work in the city.

On March 26, 1853, Denis married Mary Barry, a distant cousin who also emigrated from Ireland. It was around this time his name evolved from ‘Hegarty’ to ‘Hagerty’ and then later to ‘Haggerty’. Denis and Mary had 10 children and had a house on Thalia Street, and later moved to a bigger house on Market Street. Around this time his first name evolved to ‘Dennis’.

Dennis and his brother-in-law, David Barry began a partnership at a cotton pickery in New Orleans, when cotton accounted for three-quarters of the total trade of the city. (A pickery is an operation that rebales loose, damaged or spilled cotton samples for resale.) Eventually David broke away from the business and Dennis became sole proprietor of the pickery on Orange and Tchoupitoulas Streets (in the Lower Garden District, very close to the Mississippi River) for many years. The Haggerty Cotton Pickery originally operated with slave labor until the Union Army occupied New Orleans in late April 1862. His older sons continued the business as Dennis got older.

Dennis Barry Haggerty died at 8:30 AM on May 16, 1890. He had been a resident of New Orleans for over 40 years. He was buried at Saint Patrick’s Cemetery #2