Daily AncestorJulian calendar
The Julian calendar, introduced by Julius Caesar, adds a leap day every fourth year without exception; Britain and its colonies used it until 1752.
The Julian calendar was proposed in 46 BC by Julius Caesar and took effect in 45 BC. It has 365 days with a leap day every fourth year. That makes its average year slightly too long, so over the centuries it drifted away from the seasons.
Catholic countries replaced it from 1582, but Britain and its colonies kept it until 1752. Records from colonial America before then are in Julian dates, while records from places like New France or Spanish Florida may already use the Gregorian calendar, so two dates for the same day can differ by 10 or 11 days.
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Daily Ancestor. "Julian calendar." Dictionary of Old Record Words. https://dailyancestor.com/dictionary/dates-calendar/julian-calendar. Last checked 2026-10-01.