Two tulip poplars (Liriodendron tulipifera L.) growing at Monticello, the home of Thomas Jefferson, were recently removed because of potential damage to the house; however, their ages were uncertain. Jefferson's writings express his interest in tulip poplars and suggest that he may have planted at least one, but his documents are not conclusive. After the Thomas Jefferson Foundation purchased the property in A.D. 1923, expert opinions on the ages of these trees were divided. This study investigated the ages of both trees (referred to as northwest and southwest). Even though the southwest tree's bole was hollow and decay was present in the northwest tree, usable cross-sections were obtained. The southwest tree's cross-section was from an upper branch, whereas upper and lower cross-sections were extracted from the bole of the northwest tree. Ring widths were crossdated and statistically verified using an oak chronology from Monticello. The innermost rings of the southwest tree dated to A.D. 1852 and those of the upper and lower sections of the northwest tree dated to 1822 and 1808, respectively. These dendrochronological analyses in combination with historical photographs support the conclusion that the northwest tree and likely the southwest tree were Jefferson era, but the evidence for the southwest tree is less certain.