Methods, apparatus, systems and articles of manufacture are disclosed to estimate an audience population. An apparatus includes a characteristic identifier to determine whether respective ones of respondents are associated with a characteristic, a respondent identifier to determine whether the respective ones of the respondents are recaptured based on a comparison of a person identifier corresponding to respondents and a database of previously identified person identifiers, a count determiner to, in response to the respective ones of the respondents exhibiting the characteristic, increase a total capture count by one and, in response to detecting unique instances of the respective ones of the respondents exhibiting the characteristic, increase a unique capture count by one, and a population estimator to, in response to a recapture probability satisfying a threshold, determine a population estimate having the characteristic based on the total capture count, the unique capture count, and a number of available samples.