Best Time to Visit Castillo de San Marcos

Castillo de San Marcos National Monument is a National Monument in FL and a moderately visited park, drawing about 598,000 recreation visits in 2025. Visitation has eased over the past decade, down about 13.4%. Crowds concentrate sharply by season: March is the busiest month at about 1.5× the park's average month, while September is the calmest at roughly 0.6× — a 3-to-1 swing between high and low season. Roughly 24% of the year's visitors arrive in the three summer months of June, July and August alone, so timing a trip outside that window is the single biggest lever on how crowded the park feels. Weather swings from an average high-season warmth near 82°F in July down to about 58°F in January, with the wettest stretch in August. About 8 months a year see comfortable average temperatures in the 50–80°F range, which is part of why crowd timing and weather timing don't always line up. The sweet spot is October: pleasant weather with noticeably thinner crowds (shoulder season). Visit then and you trade a little peak-season certainty for noticeably shorter lines and easier parking than the March rush. Daylight ranges from about 10.1 hours in midwinter to 13.9 hours near the summer solstice, which shapes how much ground you can cover in a day. A standard private-vehicle entrance pass runs about $15, valid for several days, so a shoulder-season trip stretches that fee across quieter, more comfortable days. These crowd figures are drawn from 1979–2025 of National Park Service visitor-use records, paired with 1991–2020 NOAA climate normals, and are updated as new monthly data is released.