The importance of Seminole County in the history of the area lies in its location at the navigable headwaters of the St. Johns River and the elevated forest land south of the three large lakes within its boundaries: Monroe, Harney, and Jesup. Ancient Indian mounds along these waters indicate its importance before recorded history. The perfection of the steamboat in the early part of the 19th century opened the river waterways to commerce, and the banks of these lakes became the staging points for the Second Seminole Indian War (1835-42).
At the conclusion of the Civil War immigration to the area accelerated, lumbering of the virgin cypress and pine began, and large citrus groves were planted. Regular steamboat travel along the St. Johns River to Sanford was established by the 1850's. The coming of the railroads to the area in the early 1880's connected the port of Sanford with small settlements to the south and the area became a tourist mecca for winter visitors.
By 1887 large hotels welcomed visitors in Sanford, Longwood, Altamonte Springs, and points farther south. Travel time by rail from New York City was only 44 hours.
Back-to-back freezes in December 1894 and February 1895 destroyed the citrus industry of the region, but by the early part of the 20th century it was flourishing again, as were large celery and vegetable farms, and dairy and cattle industries.
Sanford, founded by Henry S. Sanford in 1870, became the county seat in 1913 when Seminole County was separated from Orange County. During the latter part of the 20th century the agricultural activities gradually began to be replaced by offices, light industry, and home sites for people who continue to find Seminole County an attractive place to work and reside. Both Sanford and Longwood have historic districts which are listed on the National Register of Historic Places.