Introduction: The Supplemental Nutrition Assistance Program (SNAP) plays an important role in shaping the diet of low-income individuals and families. Trends in ultra-processed food intake (UPF) among SNAP participants and non-participants has not been studied. Hypothesis: Compared to non-participants, SNAP participants would have a higher UPF intake; purchases would be larger for foods from SNAP-eligible versus ineligible venues. Methods: Data from NHANES survey cycles 2003-2004 through 2017-2018 were used. Dietary recalls from individuals ≥1 year of age were categorized according to Nova classification. Venues from which individuals reported buying food were grouped as SNAP-eligible (ex. grocery/supermarkets, convenience stores) or SNAP-ineligible venues (ex. restaurant/cafeteria). SNAP participation status was self-reported and categorized as SNAP participants; income-eligible nonparticipants (no SNAP + family income ≤130% of federal poverty line, FPL); lower-income, ineligible non-participants (no SNAP + family income >130% - ≤300% of FPL); higher-income ineligible non-participants (no SNAP + family income >300% FPL). UPF (% of total daily kcal) across eight survey cycles was examined using multivariable linear regression, stratified by SNAP participation status. Heterogeneous trends across SNAP participation status were tested by Wald F models. Trends were examined for UPF purchased from different venues. Analyses were conducted in youths (ages 1-19) and adults (≥ 20), separately. Results: The sample included 54979 participants from 2003-2004 through 2017-2018. The % of energy from UPF increased over time in both youth (Δ 2018-2003 , 4.3%; 95% CI, 2.9% - 5.8%; P linear trend < .001) and adults (Δ 2018-2003 , 2.5%; 95% CI, 0.2% - 4.9%; P linear trend = .002). There were no differences between SNAP participants, income-eligible non-participants, lower-income ineligible and higher-income non-participants. The mean contribution of UPF from SNAP-eligible venues decreased in both youth (Δ 2018-2003 , -2.6%; 95% CI, -6.1% - 0.9%; P linear trend = .001) and adults (Δ 2018-2003 , -2.3%; 95% CI, -5.0% - 0.8%; P cubic trend < .001) with no differences by SNAP participation. UPF purchases from fast-food restaurants increased in youth (Δ 2018-2003 , 2.2%; 95% CI, -0.4% - 4.8%; P quadratic trend = .036) and adults (Δ 2018-2003 , 2.9%; 95% CI, 0.6% - 5.1%; P cubic trend = .007), while those from schools remained unchanged. There were no differences by SNAP participation status. Conclusions: Total UPF consumption increased between 2003-2004 and 2017-2018 and were seen among both participants of SNAP and among income-eligible and ineligible non-participants. UPF were increasingly sourced from SNAP ineligible venues. SNAP benefit allotments should account for secular changes in dietary patterns by enabling the purchase of healthier processed and prepared foods.