| 1803 November 1 |
Born near St. Francisville in West Feliciana Parish. He is the fourth son of John Hunter Johnson and Thenia Munson at his father’s plantation Troy. His grandfather arrived in the area in the 1770s. His father had a leading role in the West Florida Rebellion and served as a British officer in Natchez during the English occupation and later became a lawyer, planter, parish sheriff and judge, finally settling at Fairview Plantation on Bayou Sara. Isaac was taught by private tutors early and read law under his father and his uncle Joseph E. Johnson. |
| 1828 | Establishes his own law practice then joins his uncle and brothers as a partner. Marries Charlotte McDermott. |
| 1833 | Becomes involved in local Democratic politics and wins a seat in the State House of Representatives, leaving at the end of his first term. |
| 1839 | Appointed a judge in what was, at that time, the 3rd. Judicial Court. |
| 1845 | Nominated by Democratic Party to run for governor against Whig William De Buys. |
| 1846 January 19 |
The campaign is unremarkable and Johnson wins by 2,491 votes. |
| 1846 February 12 |
Assumes office of governor at age 43 years. The new constitution created last year fills his administration with much turmoil and debate. Even his inaugural oath is questioned. In his speech Johnson calls for moving the capital and stresses the public school laws. |
| 1846-1848 |
War between the U.S. and Mexico. Johnson puts out a call for volunteers and has words with the Army Paymaster over maintenance of the volunteers. He wants to annex all of Mexico. The next controversy is expansion of slavery to new territories. Johnson is a champion of state's rights, he denounces the Wilmot Proviso, by David Wilmot to prohibit slavery in territories. Taylor Democrats carry the state for the Whigs in the presidential election. |
| 1847 | Charlotte Johnson dies leaving 3 children. His second marriage will be one of convenience. |
| 1848 | 1848 Johnson’s leadership is a disappointment to state Democratic leaders because he appoints Whigs to office and did not like strict party disciplines. By 1848 he has fallen out of favor. |
| 1849 | Move to new capital. |
| 1850 January 28 |
The legislature completes its move to Baton Rouge. Johnson requests money for levees damaged in the 1849 floods. Johnson retires from office. |
| 1850 February 15 |
His successor in the governor’s office, Joseph Marshall Walker, appoints him as Attorney General and he serves well in several important cases. |
| 1850-1854 | Louisiana State Attorney General |
| 1852 | Returns to his estate in West Feliciana Parish. |
| 1853 | Runs as a candidate for Associate Justice of the State Supreme Court. |
| 1853 March 15 |
Dies from a heart attack at the Verandah Hotel in New Orleans and is buried at Troy Plantation. Two of his sons die of yellow fever later this year. |