Lathrop was the son of Azel and Rosanna Holland Lathrop of New York. Azel, a railroad engineer, moved the family to Michigan's upper peninsula when Frank was an infant. Frank followed his father in the railroad business and married the former Effie Winona Woodin of Wisconsin. The couple eventually moved to St Clair County, and Lathrop opened a lumber mill at Riverside. With his output in great demand in the growing city of Birmingham, Lathrop opened a business office and moved his family to a house at 819 30th Street South in Highland Park. Effie died shortly after the birth of their third child in 1890.
Lathrop then married the former Annie Love King of Georgia and had two more children before she died in 1900. On September 17, 1902 Lathrop remarried again, to Sally Comer, the daughter of former Governor B. B. Comer and widow of Judge James Blount Jr. He completed construction of a grand new residence on 14th Avenue South in 1904.
In Birmingham, Lathrop was involved in Republican Party politics and was a delegate to five national party conventions. He ran to succeed Representative Milford Howard of Alabama's 7th District in the U.S. House of Representatives in the 1898 election, but finished third behind Democrat John Burnett and Populist Oliver Street. Much later, he challenged incumbent Tom Heflin for U.S. Senate in the 1924 election, and six-term incumbent George Huddleston of 9th District in the 1926 election. He garnered almost 25% of the vote in the 1924 Senate campaign, but only 5% of votes in the 1926 Congressional race.
- Frank Lathrop at findagrave.com