Introduction: Fertility is the major component of population dynamics and plays an important role in affecting the size and structure of a particular population. In Ethiopia, the total fertility rate is 4.6 children per woman. This high fertility could bring a significant problem on the health of mothers and children. Factors such as under-five child mortality, age at first marriage, age at first birth, income, place of residency, contraceptive use were associated with fertility level. However, studies addressing magnitude of fertility and associated factors are scarce in the study area. Objectives: This study was conducted to determine the magnitude and factors associated with fertility among ever-married women in Wondo district, Oromia, Ethiopia. Methods: A community based cross-sectional study was conducted on randomly selected 1266 subjects in Wondo district using an interviewer-administered questionnaire. A stratified sampling technique was used to draw the study participants. Data were collected using a pretested and structured questionnaire from March 15 to April 15, 2019. The collected data were coded, entered, and cleaned. Bivariate and multivariable logistic regression analyses were used to identify significant factors. Women who ever born 5 or greater alive (CEB)children were categorized as having high fertility and women with less than 5 children ever born alive (CEB) were categorized as having low fertility. Results: This study showed that 40.6% (95% CI: 37.9%-43.3%) of the respondents had high fertility. Age at first marriage less than 18years (AOR=2.63,95% CI:1.53, 4.53),history of under-five child mortality (AOR=3.57,95% CI:1.88, 6.78),being housewives (AOR=5.65,95% CI:2.86, 11.14), sex preference (AOR=6.65,95% CI:2.08, 21.25) and never used contraceptive methods (AOR=5.87,95% CI:3.76,9.17) were significantly associated with high fertility. Conclusion: About 40% of the respondents had high fertility. Women’s occupation, educational status, age at first marriage, age at first birth, sex preference, perceive family size, contraceptive ever use, history of abortion and history of under-five child mortality were associated with high fertility. Thus, reduction of under-five mortality, delaying age at first marriage and birth, reducing women’s illiteracy, empowering and creating job opportunity for women could help in reducing high fertility.