The city was founded by John C. Williams from Detroit, who purchased land here in 1876, and Peter Dementyev, who built a railway station in 1888. St. Petersburg was officially registered on February 29, 1892, with a population of about 300 people. The city was named after Saint Petersburg, Dementyev's hometown and the capital of the Russian Empire. According to local legend, Williams and Dementyev drew lots to decide who would name the city. The winner, Peter Dementyev, chose the name in honor of Saint Petersburg, while Williams named the first hotel after Detroit, his hometown. This hotel, 'Detroit,' still exists in the business part of the city and is now a condominium.

American explorers describe the incredible difficulties they faced while building the railway. All materials and products had to be delivered from afar, clearing the land, building bridges, and traversing jungles filled with alligators, poisonous snakes, and mosquitoes. Because of this, especially during the tropical rainy season, workers fell ill with tropical yellow fever. Financial difficulties also plagued them: there was not enough money to pay off debts to creditors and salaries to workers. At a critical moment, an angry mob of workers even wanted to lynch Dementyev. Partners suggested he stop construction and abandon the railway project to Tampa Bay, as stated in the 'Notes of the Russian Academic Group in the USA,' which describes Dementyev's history. Despite all the challenges, Dementyev fulfilled his dream by completing the construction: on July 8, 1888, the first train arrived on the railway from Sanford to St. Petersburg, spanning 150 miles.

Today, it is a modern and well-equipped city with a population of about a quarter of a million people. It is called the Sunshine City, as St. Petersburg enjoys good weather for about 360 days a year. Because of this, it is popular among tourists, especially from northern states with cold climates.