Geronimo Blanchard was born about 1766 in Baltimore, Maryland, and christened with the French name of Jerome. His parents, French Acadians, were deported to Maryland from Nova Scotia about 1755 as part of the British Le Grand Derangement. He is the son of patriot Enselme Blanchard. Geronimo arrived in Louisiana with his parents in 1767. (At the time, the territory was called Spanish Louisiana as Spain had previously acquired the territory from France in the Treaty of Paris of 1763. Spain, shortly after the acquisition, began to offer land grants to entice settlers to the territory.)

In August 1779, to slow the British expansion in the Spanish Louisiana Territory, Governor General Bernardo de Gálvez of Spanish Louisiana had started to assemble a diverse army of more than 600 men, speaking more than 10 languages, including Geronimo Blanchard, who was about age 13 at the time.

In early September 1779 the Gálvez army began a march of more than 100 miles, through dense Louisiana forests and swamps, to challenge the British at Ft. Bute of Manchak, a six-cannon British stockade fort a few miles northwest of New Orleans. The Gálvez army reached the outskirts of Fort Bute on 06 Sept 1779. Lightly manned by the British on that date, Fort Bute was taken in a dawn attack on 07 Sept 1779. One British defender was killed, two dozen captured, and six escaped to the British fort at Baton Rouge, Louisiana. The Gálvez army suffered no casualties in this engagement.

Gálvez, after resting his men, marched about fifteen miles to the British fort at Baton Rouge and reached the outskirts of the fort on 12 September 1779 to lay siege. The fort, surrounded by a 9-foot-deep and 18-foot wide moat, was manned by a British force of about 550 men with 13 cannons. On 21 September 1779 the Gálvez army launched a three-hour artillery barrage from a secure vantage point shielded by substantial foliage that could not be impacted by the massive volley of British artillery. By midday the British surrendered, the terms of which included the surrender of both Baton Rouge and Fort Panmure, at Natchez, Mississippi. The British suffered 4 casualties, 2 wounded, and 375 captured. Thirty later died from their wounds while in captivity. The army of Gálvez suffered one casualty and two wounded.

The army of Gálvez, including Geronimo, sailed from New Orleans in early January of 1780 to capture the British Fort Charlotte at Mobile with a force that now numbered about 1200 men plus reinforcements from Havana, Cuba. After a month-long siege the Gálvez Spanish artillery battery began firing at Fort Charlotte and inflicted heavy damage. The British surrendered on 14 March 1780 after suffering 20 casualties. The Gálvez army suffered 14 killed and 23 wounded.

On 11 February 1787, Geronimo married Marina Clouatre in St. Gabriel Catholic Church, St. Gabriel, Spanish Louisiana. Marina was the daughter of Pedro Clouatre, also a deported French Acadian. Geronimo continued to serve in the local militia following the battle of Fort Charlotte. He died on 12 March 1792 in St. Gabriel, Iberville Parish, Spanish Louisiana, at the young age of 27.

The archived Service Sheet documents in Simancas, Spain, dated 12 June 1792, states the following in Ledger 7291:

Note: AGS: Archivo General de Simancas, Simancas, Spain.

Of interest is that in a secret treaty of 1801, Spain sold the Louisiana Territory back to France. Needing the money in 1803, France sold the 828,000 square mile territory to the United States for $50 Million Francs and the cancellation of $18 Million Francs in debt.