Highly pathogenic avian influenza (HPAI) A(H5N1) virus, clade 2.3.4.4b, genotype 3.13, was first confirmed in dairy cattle in March 2024 in a Texas dairy herd and has since spread to other states, likely via movement of subclinically affected cattle. On 2024 May 5, a backyard poultry farm in Idaho reported sick and dying chickens. This pasture-based farm included 1,100 chickens, 32 ducks, 18 alpacas, 13 yaks, 3 cats, 3 dogs, 1 llama, and 1 goat. Most animals had direct access to a pond filled by the stream bordering the property. Additional dairy premises in the same county had been confirmed with HPAI during the same timeframe. The poultry were depopulated on May 10, the same day the first alpaca abortion was observed. Overall, 4 abortions occurred among the alpacas. In one of the abortions, HPAI A(H5N1) virus was isolated from fetal tissues. Additional testing documented seroconversion in several alpacas and detection of HPAI A(H5N1) virus in milk from an alpaca with a cria. To our knowledge, HPAI A(H5N1) virus, clade 2.3.4.4b, has not been reported previously in alpacas.