Old Monroe is a city in Lincoln County, Missouri, United States. Old Monroe was the site of Fort Howard. It was laid out in 1819, and named for President James Monroe. The name was prefixed with “Old” in order to avoid postal conflict with Monroe City, Missouri. The city was originally named “Monroe” and it served as the county seat from 1819 until 1823. The name would change to its current form around 1857 when Monroe County and its county seat, Monroe City, were established. The postal office then labeled the older town as Old Monroe.
The median income for a household in the city was $31,429, and the median income for a family was $42,188. Males had a median income of $39,063 versus $21,964 for females. The per capita income for the city was $15,457. None of the families and 4.5% of the population were living below the poverty line, including no under eighteens and 5.6% of those over 64.